[renovate]

Note

This PR body was truncated due to platform limits.

This PR contains the following updates:

Package	Change	Age	Confidence
qs	^6.14.0 → ^6.17.1

---

qs's arrayLimit bypass in its bracket notation allows DoS via memory exhaustion

CVE-2025-15284 / GHSA-6rw7-vpxm-498p

More information

Details

Summary

The arrayLimit option in qs did not enforce limits for bracket notation (a[]=1&a[]=2), only for indexed notation (a[0]=1). This is a consistency bug; arrayLimit should apply uniformly across all array notations.

Note: The default parameterLimit of 1000 effectively mitigates the DoS scenario originally described. With default options, bracket notation cannot produce arrays larger than parameterLimit regardless of arrayLimit, because each a[]=value consumes one parameter slot. The severity has been reduced accordingly.

Details

The arrayLimit option only checked limits for indexed notation (a[0]=1&a[1]=2) but did not enforce it for bracket notation (a[]=1&a[]=2).

Vulnerable code (lib/parse.js:159-162):

if (root === '[]' && options.parseArrays) {
    obj = utils.combine([], leaf);  // No arrayLimit check
}

Working code (lib/parse.js:175):

else if (index <= options.arrayLimit) {  // Limit checked here
    obj = [];
    obj[index] = leaf;
}

The bracket notation handler at line 159 uses utils.combine([], leaf) without validating against options.arrayLimit, while indexed notation at line 175 checks index <= options.arrayLimit before creating arrays.

PoC

const qs = require('qs');
const result = qs.parse('a[]=1&a[]=2&a[]=3&a[]=4&a[]=5&a[]=6', { arrayLimit: 5 });
console.log(result.a.length);  // Output: 6 (should be max 5)

Note on parameterLimit interaction: The original advisory's "DoS demonstration" claimed a length of 10,000, but parameterLimit (default: 1000) caps parsing to 1,000 parameters. With default options, the actual output is 1,000, not 10,000.

Impact

Consistency bug in arrayLimit enforcement. With default parameterLimit, the practical DoS risk is negligible since parameterLimit already caps the total number of parsed parameters (and thus array elements from bracket notation). The risk increases only when parameterLimit is explicitly set to a very high value.

Severity

• CVSS Score: 6.3 / 10 (Medium)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:L

References

• https://github.com/ljharb/qs/security/advisories/GHSA-6rw7-vpxm-498p
• https://nvd.nist.gov/vuln/detail/CVE-2025-15284
• https://github.com/ljharb/qs/commit/3086902ecf7f088d0d1803887643ac6c03d415b9
• https://github.com/advisories/GHSA-6rw7-vpxm-498p

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

---

qs's arrayLimit bypass in comma parsing allows denial of service

CVE-2026-2391 / GHSA-w7fw-mjwx-w883

More information

Details

Summary

The arrayLimit option in qs does not enforce limits for comma-separated values when comma: true is enabled, allowing attackers to cause denial-of-service via memory exhaustion. This is a bypass of the array limit enforcement, similar to the bracket notation bypass addressed in GHSA-6rw7-vpxm-498p (CVE-2025-15284).

Details

When the comma option is set to true (not the default, but configurable in applications), qs allows parsing comma-separated strings as arrays (e.g., ?param=a,b,c becomes ['a', 'b', 'c']). However, the limit check for arrayLimit (default: 20) and the optional throwOnLimitExceeded occur after the comma-handling logic in parseArrayValue, enabling a bypass. This permits creation of arbitrarily large arrays from a single parameter, leading to excessive memory allocation.

Vulnerable code (lib/parse.js: lines ~40-50):

if (val && typeof val === 'string' && options.comma && val.indexOf(',') > -1) {
    return val.split(',');
}

if (options.throwOnLimitExceeded && currentArrayLength >= options.arrayLimit) {
    throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');
}

return val;

The split(',') returns the array immediately, skipping the subsequent limit check. Downstream merging via utils.combine does not prevent allocation, even if it marks overflows for sparse arrays.This discrepancy allows attackers to send a single parameter with millions of commas (e.g., ?param=,,,,,,,,...), allocating massive arrays in memory without triggering limits. It bypasses the intent of arrayLimit, which is enforced correctly for indexed (a[0]=) and bracket (a[]=) notations (the latter fixed in v6.14.1 per GHSA-6rw7-vpxm-498p).

PoC

Test 1 - Basic bypass:

npm install qs

const qs = require('qs');

const payload = 'a=' + ','.repeat(25);  // 26 elements after split (bypasses arrayLimit: 5)
const options = { comma: true, arrayLimit: 5, throwOnLimitExceeded: true };

try {
  const result = qs.parse(payload, options);
  console.log(result.a.length);  // Outputs: 26 (bypass successful)
} catch (e) {
  console.log('Limit enforced:', e.message);  // Not thrown
}

Configuration:

• comma: true
• arrayLimit: 5
• throwOnLimitExceeded: true

Expected: Throws "Array limit exceeded" error.
Actual: Parses successfully, creating an array of length 26.

Impact

Denial of Service (DoS) via memory exhaustion.

Suggested Fix

Move the arrayLimit check before the comma split in parseArrayValue, and enforce it on the resulting array length. Use currentArrayLength (already calculated upstream) for consistency with bracket notation fixes.

Current code (lib/parse.js: lines ~40-50):

if (val && typeof val === 'string' && options.comma && val.indexOf(',') > -1) {
    return val.split(',');
}

if (options.throwOnLimitExceeded && currentArrayLength >= options.arrayLimit) {
    throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');
}

return val;

Fixed code:

if (val && typeof val === 'string' && options.comma && val.indexOf(',') > -1) {
    const splitArray = val.split(',');
    if (splitArray.length > options.arrayLimit - currentArrayLength) {  // Check against remaining limit
        if (options.throwOnLimitExceeded) {
            throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');
        } else {
            // Optionally convert to object or truncate, per README
            return splitArray.slice(0, options.arrayLimit - currentArrayLength);
        }
    }
    return splitArray;
}

if (options.throwOnLimitExceeded && currentArrayLength >= options.arrayLimit) {
    throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');
}

return val;

This aligns behavior with indexed and bracket notations, reuses currentArrayLength, and respects throwOnLimitExceeded. Update README to note the consistent enforcement.

Severity

• CVSS Score: 3.7 / 10 (Low)
• Vector String: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

References

• https://github.com/ljharb/qs/security/advisories/GHSA-w7fw-mjwx-w883
• https://nvd.nist.gov/vuln/detail/CVE-2026-2391
• https://github.com/ljharb/qs/commit/f6a7abff1f13d644db9b05fe4f2c98ada6bf8482
• https://github.com/advisories/GHSA-w7fw-mjwx-w883

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

---

qs has a remotely triggerable DoS: qs.stringify crashes with TypeError on null/undefined entries in comma-format arrays when encodeValuesOnly is set

CVE-2026-8723 / GHSA-q8mj-m7cp-5q26

More information

Details

Summary

qs.stringify throws TypeError when called with arrayFormat: 'comma' and encodeValuesOnly: true on an array containing null or undefined. The throw is synchronous and not handled by any of qs's null-related options (skipNulls, strictNullHandling).

Details

In the comma + encodeValuesOnly branch, lib/stringify.js:145 mapped the array through the raw encoder before joining:

obj = utils.maybeMap(obj, encoder);

utils.encode (lib/utils.js:195) reads str.length with no null guard, so a null or undefined element throws TypeError. skipNulls and strictNullHandling are both checked in the per-element loop below this line and never get a chance to run.

Same class of bug as the filter-array path fixed in 0c180a4. The vulnerable shape of the comma + encodeValuesOnly branch was introduced in 4c4b23d ("encode comma values more consistently", PR #​463, 2023-01-19), first released in v6.11.1.

PoC

const qs = require('qs');

qs.stringify({ a: [null, 'b'] },      { arrayFormat: 'comma', encodeValuesOnly: true });
qs.stringify({ a: [undefined, 'b'] }, { arrayFormat: 'comma', encodeValuesOnly: true });
qs.stringify({ a: [null] },           { arrayFormat: 'comma', encodeValuesOnly: true });
// TypeError: Cannot read properties of null (reading 'length')
//     at encode (lib/utils.js:195:13)
//     at Object.maybeMap (lib/utils.js:322:37)
//     at stringify (lib/stringify.js:145:25)

Fix

lib/stringify.js:145, applied in 21f80b3 on main:

- obj = utils.maybeMap(obj, encoder);
+ obj = utils.maybeMap(obj, function (v) {
+     return v == null ? v : encoder(v);
+ });

null and undefined now pass through maybeMap unchanged and reach the join(',') step as-is. For { a: [null, 'b'] } this produces a=,b, matching the non-encodeValuesOnly comma path (which already joins before encoding and produces a=%2Cb for the same input). Single-element [null] arrays still collapse via the existing obj.join(',') || null and remain subject to skipNulls / strictNullHandling in the main loop.

Affected versions

>=6.11.1 <=6.15.1

The vulnerable code shape was introduced in 4c4b23d and first shipped in v6.11.1. Earlier versions — including all of 6.7.x, 6.8.x, 6.9.x, 6.10.x, and 6.11.0 — implemented the comma + encodeValuesOnly path differently (joining before encoding) and are not affected. Empirically verified across released versions.

Impact

Application code that calls qs.stringify with both arrayFormat: 'comma' and encodeValuesOnly: true (both non-default) on input that may contain a null or undefined array element will throw synchronously instead of producing a query string. In a typical Node.js HTTP framework (Express, Fastify, Koa, hapi) the sync throw is caught by the framework's error boundary and the affected request returns a 500; the worker process does not exit and subsequent requests are unaffected. The "kills the worker process" framing applies only to call sites outside a request-handler error boundary (background jobs, startup paths, stream pipelines) or to deployments with framework error handling explicitly disabled.

The vulnerable input is a null or undefined entry inside an array; this is reachable from JSON request bodies or from application code constructing arrays from user input, but not from standard HTML form submissions (which produce strings or omitted fields, not literal null).

Severity

• CVSS Score: 6.3 / 10 (Medium)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

References

• https://github.com/ljharb/qs/security/advisories/GHSA-q8mj-m7cp-5q26
• https://nvd.nist.gov/vuln/detail/CVE-2026-8723
• https://github.com/ljharb/qs/commit/21f80b33e5c8b3f7eba1034fff0da4a4a37a1d41
• https://github.com/advisories/GHSA-q8mj-m7cp-5q26

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

---

qs: Denial of Service via Attacker Controlled isBuffer

CVE-2026-82417 / GHSA-4mjr-xmp4-gh2g

More information

Details

Summary

qs.stringify() calls utils.isBuffer() on every value it serializes, and utils.isBuffer() invokes obj.constructor.isBuffer(obj) without checking that it is callable. A value whose own constructor.isBuffer is a non-function makes qs call a non-callable and throw TypeError. Such a value is produced by qs.parse itself from an untrusted query string when plainObjects: true or allowPrototypes: true is set, so a pure-qs parse → stringify round-trip — no JSON.parse — turns an unauthenticated query string into an uncaught throw.

An attacker-controlled parse input reaches the host application's availability asset — via qs's own recommended plainObjects mitigation — and triggers an uncaught exception during a parse → stringify round-trip.

Details

utils.isBuffer runs at lib/stringify.js:127 for every serialized value:

if (isNonNullishPrimitive(obj) || utils.isBuffer(obj)) { ... }

utils.isBuffer (lib/utils.js:327-333) invokes obj.constructor.isBuffer without verifying it is callable:

var isBuffer = function isBuffer(obj) {
    if (!obj || typeof obj !== 'object') { return false; }
    return !!(obj.constructor && obj.constructor.isBuffer && obj.constructor.isBuffer(obj));
};

constructor and isBuffer are ordinary keys. qs.parse with plainObjects: true or allowPrototypes: true keeps them as own properties, so the parsed value carries a non-function constructor.isBuffer; stringify then calls a non-callable and throws TypeError. By contrast utils.isRegExp uses a brand check (Object.prototype.toString); the missing guard here is an internal inconsistency, not a platform limitation.

Trust Boundary Note

qs.stringify alone treats its input as caller-constructed, so serializing a hostile object could be argued outside its contract. This report does not depend on that framing: the malicious shape is produced by qs.parse, whose input is untrusted by design. qs.parse normally strips a constructor key via its prototype guard, but with the documented options plainObjects: true or allowPrototypes: true the key survives and lands as an own property. Feeding the parsed object back into qs.stringify — the standard round-trip in gateways and request-forwarders — then hits the unchecked call.

PoC

poc02c_isBuffer_qs_only_roundtrip.js — pure-qs chain, no JSON.parse; an untrusted query string alone reaches the throw:

'use strict';
var qs = require('qs');

var untrustedQueryString = 'x%5Bconstructor%5D%5BisBuffer%5D=y'; // x[constructor][isBuffer]=y

var parsed = qs.parse(untrustedQueryString, { plainObjects: true });
console.log('[parse] kept constructor key:', JSON.stringify(parsed));

try {
    qs.stringify(parsed);
    console.log('[stringify] no throw (unexpected)');
} catch (e) {
    console.log('[stringify] DoS reproduced ->', e.constructor.name + ':', e.message);
}

poc02_isBuffer.js — the minimal defect:

'use strict';
var qs = require('qs');
try {
    qs.stringify(JSON.parse('{"a":{"constructor":{"isBuffer":"x"}}}'));
} catch (e) {
    console.log('[A] DoS reproduced ->', e.constructor.name + ':', e.message);
}

poc02b_isBuffer_async_crash.js — worker death in an async sink:

'use strict';
var qs = require('qs');

function handleRequestAsync(clientJsonBody) {
    try {
        setImmediate(function () {                 // async continuation, outside the try
            qs.stringify(JSON.parse(clientJsonBody)); // throws here, uncaught
        });
        console.log('[handler] returned 200 synchronously; async work scheduled');
    } catch (e) {
        console.log('[handler] caught synchronously (will NOT happen):', e.message);
    }
}
process.on('exit', function (code) {
    console.log('[proc] process exiting with code:', code);
});
handleRequestAsync('{"filters":{"constructor":{"isBuffer":"x"}}}');

Execution Steps

cd poc
npm install qs@6.15.3
node poc02c_isBuffer_qs_only_roundtrip.js  # pure qs parse->stringify -> TypeError
node poc02_isBuffer.js                      # minimal defect -> TypeError inside stringify
node poc02b_isBuffer_async_crash.js         # async sink -> uncaught throw -> exit code 1

Reproduction Evidence

poc02c_isBuffer_qs_only_roundtrip.js :

[parse] kept constructor key: {"x":{"constructor":{"isBuffer":"y"}}}
[stringify] DoS reproduced -> TypeError: obj.constructor.isBuffer is not a function

poc02_isBuffer.js:

[A] DoS reproduced -> TypeError: obj.constructor.isBuffer is not a function

poc02b_isBuffer_async_crash.js :

[handler] returned 200 synchronously; async work scheduled
[proc] process exiting with code: 1
TypeError: obj.constructor.isBuffer is not a function
    at Object.isBuffer (.../qs/lib/utils.js:332:78)
    at stringify (.../qs/lib/stringify.js:127:45)
=== EXIT CODE: 1 ===

The pure-qs round-trip shows the malicious shape originates from qs.parse of an untrusted query string, with no JSON.parse. The synchronous try/catch in the async case does not catch the throw; the process exits with code 1, denying service to all requests on that worker.

Impact

An unauthenticated request degrades any endpoint that re-serializes deserialized client data with qs.stringify. The primary impact is a per-request failure: the handler throws and the framework returns HTTP 500. Where the call sits in an unguarded async continuation, the throw escapes and the worker process exits, denying service to all requests it was handling, which means a higher impact that depends on the application's error handling, not on qs.

Recommended Fix

Replace the duck-type with a brand check mirroring utils.isRegExp:

var isBuffer = function isBuffer(obj) {
    if (!obj || typeof obj !== 'object') { return false; }
    if (typeof Buffer !== 'undefined' && typeof Buffer.isBuffer === 'function') {
        return Buffer.isBuffer(obj);
    }
    return Object.prototype.toString.call(obj) === '[object Uint8Array]';
};

If duck-typing must remain, require typeof obj.constructor.isBuffer === 'function' before invoking and wrap the call in try/catch.

Severity

• CVSS Score: 6.3 / 10 (Medium)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

References

• https://github.com/ljharb/qs/security/advisories/GHSA-4mjr-xmp4-gh2g
• https://nvd.nist.gov/vuln/detail/CVE-2026-82417
• https://github.com/ljharb/qs/commit/e83d321ffafb38cf210683ac31714fce6ce1c6c6
• https://github.com/advisories/GHSA-4mjr-xmp4-gh2g

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

---

qs's arrayLimit bypass in its bracket notation allows DoS via memory exhaustion

CVE-2025-15284 / GHSA-6rw7-vpxm-498p

More information

Details

Summary

The arrayLimit option in qs did not enforce limits for bracket notation (a[]=1&a[]=2), only for indexed notation (a[0]=1). This is a consistency bug; arrayLimit should apply uniformly across all array notations.

Note: The default parameterLimit of 1000 effectively mitigates the DoS scenario originally described. With default options, bracket notation cannot produce arrays larger than parameterLimit regardless of arrayLimit, because each a[]=value consumes one parameter slot. The severity has been reduced accordingly.

Details

The arrayLimit option only checked limits for indexed notation (a[0]=1&a[1]=2) but did not enforce it for bracket notation (a[]=1&a[]=2).

Vulnerable code (lib/parse.js:159-162):

if (root === '[]' && options.parseArrays) {
    obj = utils.combine([], leaf);  // No arrayLimit check
}

Working code (lib/parse.js:175):

else if (index <= options.arrayLimit) {  // Limit checked here
    obj = [];
    obj[index] = leaf;
}

The bracket notation handler at line 159 uses utils.combine([], leaf) without validating against options.arrayLimit, while indexed notation at line 175 checks index <= options.arrayLimit before creating arrays.

PoC

const qs = require('qs');
const result = qs.parse('a[]=1&a[]=2&a[]=3&a[]=4&a[]=5&a[]=6', { arrayLimit: 5 });
console.log(result.a.length);  // Output: 6 (should be max 5)

Note on parameterLimit interaction: The original advisory's "DoS demonstration" claimed a length of 10,000, but parameterLimit (default: 1000) caps parsing to 1,000 parameters. With default options, the actual output is 1,000, not 10,000.

Impact

Consistency bug in arrayLimit enforcement. With default parameterLimit, the practical DoS risk is negligible since parameterLimit already caps the total number of parsed parameters (and thus array elements from bracket notation). The risk increases only when parameterLimit is explicitly set to a very high value.

Severity

• CVSS Score: 6.3 / 10 (Medium)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:L

References

• https://github.com/ljharb/qs/security/advisories/GHSA-6rw7-vpxm-498p
• https://nvd.nist.gov/vuln/detail/CVE-2025-15284
• https://github.com/ljharb/qs/commit/3086902ecf7f088d0d1803887643ac6c03d415b9
• https://github.com/ljharb/qs

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

---

qs's arrayLimit bypass in comma parsing allows denial of service

CVE-2026-2391 / GHSA-w7fw-mjwx-w883

More information

Details

Summary

The arrayLimit option in qs does not enforce limits for comma-separated values when comma: true is enabled, allowing attackers to cause denial-of-service via memory exhaustion. This is a bypass of the array limit enforcement, similar to the bracket notation bypass addressed in GHSA-6rw7-vpxm-498p (CVE-2025-15284).

Details

When the comma option is set to true (not the default, but configurable in applications), qs allows parsing comma-separated strings as arrays (e.g., ?param=a,b,c becomes ['a', 'b', 'c']). However, the limit check for arrayLimit (default: 20) and the optional throwOnLimitExceeded occur after the comma-handling logic in parseArrayValue, enabling a bypass. This permits creation of arbitrarily large arrays from a single parameter, leading to excessive memory allocation.

Vulnerable code (lib/parse.js: lines ~40-50):

if (val && typeof val === 'string' && options.comma && val.indexOf(',') > -1) {
    return val.split(',');
}

if (options.throwOnLimitExceeded && currentArrayLength >= options.arrayLimit) {
    throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');
}

return val;

The split(',') returns the array immediately, skipping the subsequent limit check. Downstream merging via utils.combine does not prevent allocation, even if it marks overflows for sparse arrays.This discrepancy allows attackers to send a single parameter with millions of commas (e.g., ?param=,,,,,,,,...), allocating massive arrays in memory without triggering limits. It bypasses the intent of arrayLimit, which is enforced correctly for indexed (a[0]=) and bracket (a[]=) notations (the latter fixed in v6.14.1 per GHSA-6rw7-vpxm-498p).

PoC

Test 1 - Basic bypass:

npm install qs

const qs = require('qs');

const payload = 'a=' + ','.repeat(25);  // 26 elements after split (bypasses arrayLimit: 5)
const options = { comma: true, arrayLimit: 5, throwOnLimitExceeded: true };

try {
  const result = qs.parse(payload, options);
  console.log(result.a.length);  // Outputs: 26 (bypass successful)
} catch (e) {
  console.log('Limit enforced:', e.message);  // Not thrown
}

Configuration:

• comma: true
• arrayLimit: 5
• throwOnLimitExceeded: true

Expected: Throws "Array limit exceeded" error.
Actual: Parses successfully, creating an array of length 26.

Impact

Denial of Service (DoS) via memory exhaustion.

Suggested Fix

Move the arrayLimit check before the comma split in parseArrayValue, and enforce it on the resulting array length. Use currentArrayLength (already calculated upstream) for consistency with bracket notation fixes.

Current code (lib/parse.js: lines ~40-50):

if (val && typeof val === 'string' && options.comma && val.indexOf(',') > -1) {
    return val.split(',');
}

if (options.throwOnLimitExceeded && currentArrayLength >= options.arrayLimit) {
    throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');
}

return val;

Fixed code:

if (val && typeof val === 'string' && options.comma && val.indexOf(',') > -1) {
    const splitArray = val.split(',');
    if (splitArray.length > options.arrayLimit - currentArrayLength) {  // Check against remaining limit
        if (options.throwOnLimitExceeded) {
            throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');
        } else {
            // Optionally convert to object or truncate, per README
            return splitArray.slice(0, options.arrayLimit - currentArrayLength);
        }
    }
    return splitArray;
}

if (options.throwOnLimitExceeded && currentArrayLength >= options.arrayLimit) {
    throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');
}

return val;

This aligns behavior with indexed and bracket notations, reuses currentArrayLength, and respects throwOnLimitExceeded. Update README to note the consistent enforcement.

Severity

• CVSS Score: 3.7 / 10 (Low)
• Vector String: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

References

• https://github.com/ljharb/qs/security/advisories/GHSA-w7fw-mjwx-w883
• https://nvd.nist.gov/vuln/detail/CVE-2026-2391
• https://github.com/ljharb/qs/commit/f6a7abff1f13d644db9b05fe4f2c98ada6bf8482
• https://github.com/ljharb/qs

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

---

qs has a remotely triggerable DoS: qs.stringify crashes with TypeError on null/undefined entries in comma-format arrays when encodeValuesOnly is set

CVE-2026-8723 / GHSA-q8mj-m7cp-5q26

More information

Details

Summary

qs.stringify throws TypeError when called with arrayFormat: 'comma' and encodeValuesOnly: true on an array containing null or undefined. The throw is synchronous and not handled by any of qs's null-related options (skipNulls, strictNullHandling).

Details

In the comma + encodeValuesOnly branch, lib/stringify.js:145 mapped the array through the raw encoder before joining:

obj = utils.maybeMap(obj, encoder);

utils.encode (lib/utils.js:195) reads str.length with no null guard, so a null or undefined element throws TypeError. skipNulls and strictNullHandling are both checked in the per-element loop below this line and never get a chance to run.

Same class of bug as the filter-array path fixed in 0c180a4. The vulnerable shape of the comma + encodeValuesOnly branch was introduced in 4c4b23d ("encode comma values more consistently", PR #​463, 2023-01-19), first released in v6.11.1.

PoC

const qs = require('qs');

qs.stringify({ a: [null, 'b'] },      { arrayFormat: 'comma', encodeValuesOnly: true });
qs.stringify({ a: [undefined, 'b'] }, { arrayFormat: 'comma', encodeValuesOnly: true });
qs.stringify({ a: [null] },           { arrayFormat: 'comma', encodeValuesOnly: true });
// TypeError: Cannot read properties of null (reading 'length')
//     at encode (lib/utils.js:195:13)
//     at Object.maybeMap (lib/utils.js:322:37)
//     at stringify (lib/stringify.js:145:25)

Fix

lib/stringify.js:145, applied in 21f80b3 on main:

- obj = utils.maybeMap(obj, encoder);
+ obj = utils.maybeMap(obj, function (v) {
+     return v == null ? v : encoder(v);
+ });

null and undefined now pass through maybeMap unchanged and reach the join(',') step as-is. For { a: [null, 'b'] } this produces a=,b, matching the non-encodeValuesOnly comma path (which already joins before encoding and produces a=%2Cb for the same input). Single-element [null] arrays still collapse via the existing obj.join(',') || null and remain subject to skipNulls / strictNullHandling in the main loop.

Affected versions

>=6.11.1 <=6.15.1

The vulnerable code shape was introduced in 4c4b23d and first shipped in v6.11.1. Earlier versions — including all of 6.7.x, 6.8.x, 6.9.x, 6.10.x, and 6.11.0 — implemented the comma + encodeValuesOnly path differently (joining before encoding) and are not affected. Empirically verified across released versions.

Impact

Application code that calls qs.stringify with both arrayFormat: 'comma' and encodeValuesOnly: true (both non-default) on input that may contain a null or undefined array element will throw synchronously instead of producing a query string. In a typical Node.js HTTP framework (Express, Fastify, Koa, hapi) the sync throw is caught by the framework's error boundary and the affected request returns a 500; the worker process does not exit and subsequent requests are unaffected. The "kills the worker process" framing applies only to call sites outside a request-handler error boundary (background jobs, startup paths, stream pipelines) or to deployments with framework error handling explicitly disabled.

The vulnerable input is a null or undefined entry inside an array; this is reachable from JSON request bodies or from application code constructing arrays from user input, but not from standard HTML form submissions (which produce strings or omitted fields, not literal null).

Severity

• CVSS Score: 6.3 / 10 (Medium)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

References

• https://github.com/ljharb/qs/security/advisories/GHSA-q8mj-m7cp-5q26
• https://nvd.nist.gov/vuln/detail/CVE-2026-8723
• https://github.com/ljharb/qs/commit/21f80b33e5c8b3f7eba1034fff0da4a4a37a1d41
• https://github.com/ljharb/qs

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

---

qs: Denial of Service via Attacker Controlled isBuffer

CVE-2026-82417 / GHSA-4mjr-xmp4-gh2g

More information

Details

Summary

qs.stringify() calls utils.isBuffer() on every value it serializes, and utils.isBuffer() invokes obj.constructor.isBuffer(obj) without checking that it is callable. A value whose own constructor.isBuffer is a non-function makes qs call a non-callable and throw TypeError. Such a value is produced by qs.parse itself from an untrusted query string when plainObjects: true or allowPrototypes: true is set, so a pure-qs parse → stringify round-trip — no JSON.parse — turns an unauthenticated query string into an uncaught throw.

An attacker-controlled parse input reaches the host application's availability asset — via qs's own recommended plainObjects mitigation — and triggers an uncaught exception during a parse → stringify round-trip.

Details

utils.isBuffer runs at lib/stringify.js:127 for every serialized value:

if (isNonNullishPrimitive(obj) || utils.isBuffer(obj)) { ... }

utils.isBuffer (lib/utils.js:327-333) invokes obj.constructor.isBuffer without verifying it is callable:

var isBuffer = function isBuffer(obj) {
    if (!obj || typeof obj !== 'object') { return false; }
    return !!(obj.constructor && obj.constructor.isBuffer && obj.constructor.isBuffer(obj));
};

constructor and isBuffer are ordinary keys. qs.parse with plainObjects: true or allowPrototypes: true keeps them as own properties, so the parsed value carries a non-function constructor.isBuffer; stringify then calls a non-callable and throws TypeError. By contrast utils.isRegExp uses a brand check (Object.prototype.toString); the missing guard here is an internal inconsistency, not a platform limitation.

Trust Boundary Note

qs.stringify alone treats its input as caller-constructed, so serializing a hostile object could be argued outside its contract. This report does not depend on that framing: the malicious shape is produced by qs.parse, whose input is untrusted by design. qs.parse normally strips a constructor key via its prototype guard, but with the documented options plainObjects: true or allowPrototypes: true the key survives and lands as an own property. Feeding the parsed object back into qs.stringify — the standard round-trip in gateways and request-forwarders — then hits the unchecked call.

PoC

poc02c_isBuffer_qs_only_roundtrip.js — pure-qs chain, no JSON.parse; an untrusted query string alone reaches the throw:

'use strict';
var qs = require('qs');

var untrustedQueryString = 'x%5Bconstructor%5D%5BisBuffer%5D=y'; // x[constructor][isBuffer]=y

var parsed = qs.parse(untrustedQueryString, { plainObjects: true });
console.log('[parse] kept constructor key:', JSON.stringify(parsed));

try {
    qs.stringify(parsed);
    console.log('[stringify] no throw (unexpected)');
} catch (e) {
    console.log('[stringify] DoS reproduced ->', e.constructor.name + ':', e.message);
}

poc02_isBuffer.js — the minimal defect:

'use strict';
var qs = require('qs');
try {
    qs.stringify(JSON.parse('{"a":{"constructor":{"isBuffer":"x"}}}'));
} catch (e) {
    console.log('[A] DoS reproduced ->', e.constructor.name + ':', e.message);
}

poc02b_isBuffer_async_crash.js — worker death in an async sink:

'use strict';
var qs = require('qs');

function handleRequestAsync(clientJsonBody) {
    try {
        setImmediate(function () {                 // async continuation, outside the try
            qs.stringify(JSON.parse(clientJsonBody)); // throws here, uncaught
        });
        console.log('[handler] returned 200 synchronously; async work scheduled');
    } catch (e) {
        console.log('[handler] caught synchronously (will NOT happen):', e.message);
    }
}
process.on('exit', function (code) {
    console.log('[proc] process exiting with code:', code);
});
handleRequestAsync('{"filters":{"constructor":{"isBuffer":"x"}}}');

Execution Steps

cd poc
npm install qs@6.15.3
node poc02c_isBuffer_qs_only_roundtrip.js  # pure qs parse->stringify -> TypeError
node poc02_isBuffer.js                      # minimal defect -> TypeError inside stringify
node poc02b_isBuffer_async_crash.js         # async sink -> uncaught throw -> exit code 1

Reproduction Evidence

poc02c_isBuffer_qs_only_roundtrip.js :

[parse] kept constructor key: {"x":{"constructor":{"isBuffer":"y"}}}
[stringify] DoS reproduced -> TypeError: obj.constructor.isBuffer is not a function

poc02_isBuffer.js:

[A] DoS reproduced -> TypeError: obj.constructor.isBuffer is not a function

poc02b_isBuffer_async_crash.js :

[handler] returned 200 synchronously; async work scheduled
[proc] process exiting with code: 1
TypeError: obj.constructor.isBuffer is not a function
    at Object.isBuffer (.../qs/lib/utils.js:332:78)
    at stringify (.../qs/lib/stringify.js:127:45)
=== EXIT CODE: 1 ===

The pure-qs round-trip shows the malicious shape originates from qs.parse of an untrusted query string, with no JSON.parse. The synchronous try/catch in the async case does not catch the throw; the process exits with code 1, denying service to all requests on that worker.

Impact

An unauthenticated request degrades any endpoint that re-serializes deserialized client data with qs.stringify. The primary impact is a per-request failure: the handler throws and the framework returns HTTP 500. Where the call sits in an unguarded async continuation, the throw escapes and the worker process exits, denying service to all requests it was handling, which means a higher impact that depends on the application's error handling, not on qs.

Recommended Fix

Replace the duck-type with a brand check mirroring utils.isRegExp:

var isBuffer = function isBuffer(obj) {
    if (!obj || typeof obj !== 'object') { return false; }
    if (typeof Buffer !== 'undefined' && typeof Buffer.isBuffer === 'function') {
        return Buffer.isBuffer(obj);
    }
    return Object.prototype.toString.call(obj) === '[object Uint8Array]';
};

If duck-typing must remain, require typeof obj.constructor.isBuffer === 'function' before invoking and wrap the call in try/catch.

Severity

• CVSS Score: 6.3 / 10 (Medium)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

References

• https://github.com/ljharb/qs/security/advisories/GHSA-4mjr-xmp4-gh2g
• https://nvd.nist.gov/vuln/detail/CVE-2026-82417
• https://github.com/ljharb/qs/commit/e83d321ffafb38cf210683ac31714fce6ce1c6c6
• https://github.com/ljharb/qs

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

---

qs : qs.stringify with arrayFormat 'comma' throws an uncaught TypeError on array elements carrying a non-callable own toString (DoS)

CVE-2026-110816 / GHSA-6pq8-jhm2-2vcw

More information

Details

Summary

qs.stringify(obj, { arrayFormat: 'comma' }) throws an uncaught TypeError: Cannot convert object to primitive value when an array in obj contains an element that carries an own, non-callable toString property (for example { a: [ { toString: 'x' } ] }). A remote, unauthenticated attacker who can influence an object that the application later re-serializes with the comma array format triggers the throw. In a service that lacks a synchronous error boundary around the serialization call, the uncaught exception crashes the worker process, producing a denial of service.

Root Cause

When arrayFormat: 'comma' is selected, the comma branch collapses the whole array into a single value via Array.prototype.join, or, under encodeValuesOnly: true, maps each element through the value encoder before joining. Both paths perform an implicit string coercion (ToPrimitive with hint "string") on each element. For an object whose own toString is a non-callable value, coercion skips the shadowed non-callable toString, falls through to Object.prototype.valueOf (which returns the object rather than a primitive), and throws. The comma branch runs this coercion before the per-element null and skip handling in the main loop, so nothing downstream can neutralize the hostile element, and the throw is never caught inside the library.

lib/stringify.js  (comma-array branch)
  line 152-154: obj = utils.maybeMap(obj, function (v) { return v == null ? v : encoder(v); });  // encodeValuesOnly path
  line 156:     objKeys = [{ value: obj.length > 0 ? obj.join(',') || null : void undefined }];   // default comma path
lib/utils.js
  line 292:     string = String(str);   // value encoder coercion reached via the encodeValuesOnly path

Impact

Prerequisites: the application calls qs.stringify with arrayFormat: 'comma' (a documented, supported option) on an object whose shape can be influenced by attacker input. Attacker-controllable sources include qs.parse(input, { allowPrototypes: true }), which retains a toString segment (Express 4's default query parser, Express 5's extended query parser, and body-parser's extended urlencoded parser all set it), qs.parse(input, { plainObjects: true }), whose null-prototype elements throw even without a toString key (eg, a[][b]=c), and JSON.parse of a request body, which needs no qs parse option at all. No authentication or user interaction is required. Demonstrated capability: a single request forces an uncaught synchronous TypeError in the serialization call. In a naive single-process Node service with no synchronous error boundary, this crashes the process and takes the service offline (availability impact). Under a framework such as Express that traps synchronous handler throws, the plausible outcome is a per-request 500 rather than a full outage; that lower-impact case is noted but not the worst credible supported deployment. There is no confidentiality or integrity impact, no memory unsafety, and no prototype pollution.

Proof of Concept

Install qs at the affected version (for example 6.16.0) and run the following script with Node.js. No network setup is required; it demonstrates the throw in isolation.

var qs = require('qs');

// Source A: qs.parse with allowPrototypes retains the hostile toString segment
qs.stringify(qs.parse('a[0][toString]=x', { allowPrototypes: true }), { arrayFormat: 'comma' });

// Source B: a JSON request body, no qs parse option needed
qs.stringify(JSON.parse('{"a":[{"toString":"x"}]}'), { arrayFormat: 'comma' });

// Also affected: the encodeValuesOnly sub-path
qs.stringify(JSON.parse('{"a":[{"toString":"x"}]}'), { arrayFormat: 'comma', encodeValuesOnly: true });

A default-join (allowPrototypes) => THREW: TypeError: Cannot convert object to primitive value
B default-join (JSON.parse) => THREW: TypeError: Cannot convert object to primitive value
C encodeValuesOnly path => THREW: TypeError: Cannot convert object to primitive value
N2 callable toString => NO THROW; output="a=z"
N3 isBuffer vector (CVE-2026-82417) => NO THROW; output="a%5Bconstructor%5D%5BisBuffer%5D=x"
qs version: 6.16.0

Attack Chain

1. Exposure: A remote, unauthenticated request reaches an endpoint whose handler eventually serializes attacker-influenced data with qs.stringify(obj, { arrayFormat: 'comma' }).
2. Control: The attacker supplies data that becomes { a: [ { toString: <non-callable value> } ] }, either via a[0][toString]=x parsed with allowPrototypes, or via a JSON body {"a":[{"toString":"x"}]}.
3. Path: In stringify, the primitive/buffer guard at lib/stringify.js:134 is false for an array, so control reaches the comma branch at lib/stringify.js:149.
4. Guard: On the encodeValuesOnly path, the closure v == null ? v : encoder(v) at lib/stringify.js:152-154 passes only null/undefined through; a non-null object still reaches the encoder. The default path skips that closure entirely and reaches obj.join(',') at lib/stringify.js:156 with no guard at all.
5. Primitive: The element is coerced to a string (Array.prototype.join, or String(str) at lib/utils.js:292). ToPrimitive skips the non-callable own toString, valueOf returns the object, and a TypeError is thrown.
6. Result: The uncaught synchronous exception propagates out of the serialization call, failing the request and, in a service without a synchronous error boundary, crashing the process (denial of service).

Bypass Evidence

This is a different element type on the code path CVE-2026-8723 (GHSA-q8mj-m7cp-5q26) patched, plus the default comma path, which that fix never covered. CVE-2026-8723 addressed a TypeError crash on null/undefined entries in the comma plus encodeValuesOnly path. Its fix (commit 21f80b3) wraps the encoder in function (v) { return v == null ? v : encoder(v); }, so it only passes null and undefined through. A non-null element with a hostile own toString fails the v == null test, so the encoder still runs and still throws; the encodeValuesOnly case (case C above) throws on the exact fixed code. The default comma path (encodeValuesOnly unset, the library default) never entered that fix at all: git log -S "obj.join(','" -- lib/stringify.js shows no security fix has ever touched the obj.join(',') line, and cases A and B throw with encodeValuesOnly unset. The related isBuffer hardening for CVE-2026-82417 (commit e83d321) is a different sink at the lib/stringify.js:134 guard, which is never entered for the array element; the negative control {a:{constructor:{isBuffer:'x'}}} serializes cleanly. Disproof attempts that failed: a valueOf-only object does not throw (it serializes to [object Object]), confirming the trigger is an element with no callable toString (an own non-callable toString, or a null-prototype object with no toString at all, as qs.parse produces under plainObjects); nested arrays ({"a":[[{"toString":"x"}]]}) throw the same way; a callable toString serializes cleanly; and the default (non-comma) array format serializes cleanly, confirming the comma format is required. All positive and negative cases were reproduced on the exact published 6.16.0 artifact.

Affected Versions

• Ecosystem: npm
• Package: qs
• Confirmed affected range: >= 6.7.0, <= 6.16.0
• Latest release checked: 6.16.0 (npm latest; git tag v6.16.0)
• Fix status: fixed in 6.16.1 (a952e75)

The arrayFormat: 'comma' join sink was introduced in qs 6.7.0, so 6.7.0 is the lower boundary; releases before 6.7.0 lack the sink. No released version fixes this vector, and the latest published release (6.16.0) reproduces the throw, so the closed upper bound <= 6.16.0 covers every affected release. The encodeValuesOnly sub-path was added later, but the default comma-join vector already affects 6.7.0, so 6.7.0 governs the lower boundary.

Suggested Fix

The comma array serialization must not allow an implicit string coercion of an array element to throw an uncaught exception. Coercion of each comma element should be performed defensively (for example by wrapping the join and per-element encode so that a coercion failure is caught and handled), and this protection must cover both the default obj.join(',') path and the encodeValuesOnly encoder path, not only the previously patched null/undefined case. As an interim mitigation without a code change, applications can avoid arrayFormat: 'comma' when serializing data derived from untrusted input, sanitize parsed objects (avoid allowPrototypes/plainObjects on untrusted input and strip unexpected own properties), or wrap qs.stringify calls in a synchronous error boundary so a coercion failure cannot crash the process.

Reported by zx (GitHub: @​manus-pi).

---

Independent report by @​Lucidsec

The following was reported separately, after this advisory, and is merged here as a duplicate.

Summary

In project qs, in versions >= 6.7.0, <= 6.16.0 (every version that supports arrayFormat: 'comma'), qs.stringify with arrayFormat: 'comma' can throw an uncaught TypeError: Cannot convert object to primitive value when an array element has a non-callable own toString. It is fixed in 6.16.1. Related: CWE-248 and CWE-704.

Technical Details

qs.stringify with arrayFormat: 'comma' joins an array at lib/stringify.js:156 via obj.join(','). An element whose own toString is not callable makes Array.prototype.join throw. There is no type check and no catch on that path.

A second path exists with encodeValuesOnly: at lib/stringify.js:151-154, maybeMap only skips v == null, then lib/utils.js:292 does String(str) and throws the same TypeError (this second site exists since v6.11.1; before that, the same input throws at join).

Who can trigger: someone who can shape an array element passed to stringify. The host must use non-default arrayFormat: 'comma'. Default arrayFormat indices does not fold arrays and is not affected. A parse-then-stringify path also needs plainObjects: true (null-prototype elements from lib/parse.js:200) or allowPrototypes: true (which Express 4's default query parser, Express 5's extended query parser, and body-parser's extended urlencoded parser all set). Default qs.parse('a[0][toString]=x') returns {} because the prototype guard drops toString. Direct JSON handed to stringify can supply {"a":[{"toString":"x"}]}.

Cause: the comma fold at lib/stringify.js:149-156 collapses the array into a single value before the main loop at lib/stringify.js:172-212, so skipNulls and strictNullHandling only ever see the joined value, never individual elements. isNonNullishPrimitive / isBuffer at lib/stringify.js:134 inspect the whole value, not each element. A normal object uses Object.prototype.toString and becomes [object Object]. An own non-callable toString is skipped, valueOf returns the object, and join throws. (The skipped TODO test at test/stringify.js:684-689 uses a plain { b: 1 } element, which does not throw; it covers the separate question of what comma format should output for object elements, not this crash.) Earlier comma crash fixes did not cover object elements.

Impact

One small input makes that serialization path throw a synchronous, catchable TypeError. Behind a framework error boundary (eg, a synchronous Express handler), the request fails with a 500 and the process survives. In a host with no error boundary (eg, a bare http.createServer handler), the uncaught exception exits the process (the client sees ECONNRESET). Availability only.

Proof of Concept

Show the proof of concept

Checked on the latest commit that was checked: 07b1d4d82c8f9301c105ea4b94fa2302cfd6e8b4. Still present. Demonstrated.

• Payload {"a":[{"toString":"x"}]} throws at lib/stringify.js:156.
• Baseline {"a":["x","y"]} returns 200 with body a=x%2Cy.
• A plain object element stringifies to a=%5Bobject%20Object%5D and does not throw.
• encodeValuesOnly: true throws via utils.js:292.
• plainObjects parse plus comma throws.

Suggested Fix

Before join, map elements with the existing primitive check; skip or replace non-primitives so join cannot throw. On the encodeValuesOnly path, do not send non-primitives into String(). Optionally guard lib/utils.js:292. Add new regression tests.

Severity

• CVSS Score: 6.3 / 10 (Medium)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

References

• https://github.com/ljharb/qs/security/advisories/GHSA-6pq8-jhm2-2vcw
• https://nvd.nist.gov/vuln/detail/CVE-2026-110816
• https://github.com/ljharb/qs/commit/a952e7519338ef0cfb25694a2988848f93333727
• https://github.com/ljharb/qs
• https://github.com/ljharb/qs/releases/tag/v6.16.1

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

---

Release Notes

ljharb/qs (qs)

v6.17.1

Compare Source

• [Fix] parse: interpretNumericEntities: decode code points above U+FFFF as surrogate pairs (#​640)
• [Fix] parse: respect plainObjects for [] with parseArrays: false (#​639)
• [Fix] utils: merge: count the elements of a sparse array against arrayLimit, not its holes
• [Fix] parse: guard bracket-wrapped prototype keys at depth 0 (#​638)
• [Refactor] parse: e

[!IMPORTANT]
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