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Quote newlines in create_process argument escaping - #22141
create_process escapes each argument with the session's to_cmd before the command reaches a shell, which is what makes passing an argument array safe against command injection. However, the Unix escape_argquote_requiring list and the Windows cmd.exeto_cmd list did not include newline, carriage return or tab.
As a result, an argument such as example.com\nid passed through unquoted, and a POSIX shell (or cmd.exe) treats the bare newline as a command separator — so the second token runs as its own command. This weakens the injection guarantee for every create_process caller whose argument can contain a newline.
For Unix this adds "\n", "\r" and "\t" to the quote_requiring list; a POSIX shell treats a newline inside single quotes as a literal, so quoting is sufficient.
For Windows this is not sufficient: cmd.exe splits its input into commands at a carriage return or line feed before it applies quoting, so a quoted newline still starts a second command on a command-shell session. The Windows to_cmd therefore rejects arguments containing \r/\n with ArgumentError rather than emitting an unsafe command line. (Thanks to CodeRabbit for catching that quoting is not enough on cmd.exe.)
The Windows argv_to_commandline path is intentionally left unchanged: it targets CreateProcess via CommandLineToArgvW, which parses an argv and does not treat line breaks as command separators, so there is no shell to inject into there.
Scope: framework escaping helpers only; no module changes.
Surfaced by CodeRabbit on #22140 (where it is correctly out of scope for that module, since the fix belongs in the shared helper).
AI tools used: Claude Code (assisted with the analysis, the fix, and the spec additions).
Verification
bundle exec rspec spec/lib/msf/base/sessions/command_shell_unix_spec.rb spec/lib/msf/base/sessions/command_shell_windows_spec.rb passes, including the new newline/CR/tab cases.
bundle exec rubocop lib/msf/base/sessions/unix_escaping.rb lib/msf/base/sessions/windows_escaping.rb adds no new offenses.
Results
bundle exec rspec on both session specs: 30 examples, 0 failures, including the new newline/CR/tab cases.
Live before/after on Linux, same cmd/unix/reverse_bash session and same payload, driving the session's real to_cmd + shell_command_token (the shell path create_process uses). The argument is x\n{touch,/tmp/pwn_nl} — a newline with no other quote-triggering character, using brace expansion so no space is needed:
before (upstream): to_cmd => echo x\n{touch,/tmp/pwn_nl} # bare newline -> /tmp/pwn_nl IS created (injection)
after (this PR): to_cmd => echo 'x\n{touch,/tmp/pwn_nl}' # quoted -> /tmp/pwn_nl is NOT created
The Windows cmd.exe path rejects line breaks and is covered by a unit spec asserting ArgumentError (no Windows target available for a live run); the argv_to_commandline path is unchanged by design.
create_process escapes each argument with the session's to_cmd before it
reaches a shell. The Unix escape_arg quote_requiring list and the Windows
cmd.exe to_cmd list did not include newline, carriage return or tab, so an
argument such as "example.com\nid" passed through unquoted and a POSIX shell
(or cmd.exe) treated the newline as a command separator, running the second
token as its own command.
Add "\n", "\r" and "\t" to the Unix list and "\n"/"\r" to the Windows
cmd.exe list (which already quotes tab and vertical tab). The Windows
argv_to_commandline path is left unchanged: it targets CreateProcess via
CommandLineToArgvW, which does not treat newlines as command separators.
Add specs covering newline, carriage return and tab for both shells.
Verified: bundle exec rspec on both session specs passes (30 examples, 0
failures), including the new cases; rubocop adds no new offenses.
No actionable comments were generated in the recent review.
Summary
Summary by CodeRabbit
Bug Fixes
Unix command arguments containing newlines, carriage returns, or tabs are now quoted when commands are constructed.
Windows command arguments containing newlines or carriage returns are rejected with an error instead of being included in a constructed command.
Other Unix and Windows argument handling remains unchanged.
Unix argument escaping now quotes arguments that contain newline, carriage return, or tab characters. Windows command conversion now raises ArgumentError when an argument contains carriage return or line feed. Specs cover both behaviors.
Changes: Shell argument escaping
Layer / File(s)
Summary
Quote Unix arguments with control characters lib/msf/base/sessions/unix_escaping.rb, spec/lib/msf/base/sessions/command_shell_unix_spec.rb
Unix escaping quotes arguments containing newline, carriage return, or tab characters. Specs check these cases.
Reject Windows arguments with line breaks lib/msf/base/sessions/windows_escaping.rb, spec/lib/msf/base/sessions/command_shell_windows_spec.rb
Windows command conversion raises ArgumentError if an argument contains carriage return or line feed. Specs check both cases.
Windows shell command construction now rejects line breaks in arguments, which closes the injection path. Callers that pass such arguments will now raise an error rather than run the command. Mergeable, with awareness that some post modules may now fail on arguments containing newlines.
Security architecture risk: Minimal · up to 5b2ac
The change strengthens shell argument handling without establishing a new security or failure-containment risk. Windows rejects line breaks before command execution, and Unix quotes the added control characters. Other command-conversion paths remain outside this fix.
Retained concerns
No architecture-level concerns identified.
Security review details
Security Blast Radius
inferred — The protection applies where executable or argument strings pass through the changed helpers before execution in an existing session. Its effective reach depends on the selected session conversion path; these shared helpers do not establish a framework-wide guarantee for every command-execution API.
Trust Boundaries and Controls
inferred — For caller-supplied strings reaching the changed shell-conversion boundary, Unix quoting keeps the added control characters within argument data, and Windows rejects CR/LF before producing a command string. The inspected Windows callers fail closed on rejection rather than dispatching the rejected command.
Pre-merge checks: 4
Check name
Status
Explanation
Title check
The title "Quote newlines in create_process argument escaping" names the main change: newline handling in shared argument escaping for create_process. The changeset quotes newline, carriage return, an…
Linked Issues check
Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check
Check skipped because no linked issues were found for this pull request.
Pr Description And Verification
The PR description explains the change and its reason: unquoted newlines let create_process arguments inject commands. It gives the verification command, expected outcomes, a concrete Linux before/a…
Full details: Title check
Explanation
The title "Quote newlines in create_process argument escaping" names the main change: newline handling in shared argument escaping for create_process. The changeset quotes newline, carriage return, and tab on Unix and rejects CR/LF on Windows. The title covers the Unix quoting part but omits the Windows rejection behavior and the tab handling, so it is partially related rather than fully descriptive. It names the affected component and the change type, which meets the title requirements.
Full details: Pr Description And Verification
Explanation
The PR description explains the change and its reason: unquoted newlines let create_process arguments inject commands. It gives the verification command, expected outcomes, a concrete Linux before/after reproduction, and an untested limit (no Windows target). The Unix part matches the diff: unix_escaping.rb adds "\n", "\r", and "\t" to quote_requiring. The standing FAIL said the Windows rejection was missing. That is no longer true. Commit 5b2ac6f ("Reject line breaks in Windows create_process args") adds a guard to WindowsEscaping#to_cmd in lib/msf/base/sessions/windows_escaping.rb. The guard raises ArgumentError when any argument matches /[\r\n]/. The Windows spec in command_shell_windows_spec.rb adds the example "should reject arguments containing line breaks". It expects ArgumentError for "a\nb" and "a\rb". The description's Windows claims now match this code and spec. The argv_to_commandline path is unchanged, as the description states. Remaining gaps are minor. The description does not cite the spec example name, and it does not report the rubocop result. The check accepts unchecked verification items. I did not run the specs, so the "30 examples, 0 failures" figure is supplied author evidence, not something I verified. The description also contains HTML-escaped > artifacts in the before/after block. None of these is a missing applicable element under this check. Prior failure addressed: Commit 5b2ac6f adds the line-break rejection to WindowsEscaping#to_cmd (raises ArgumentError for \r/\n) and changes command_shell_windows_spec.rb to expect ArgumentError for "a\nb" and "a\rb". The description's Windows claims now match the code and spec. The prior claim that no such code or spec existed is no longer true at refs/coderabbit/pre-merge-check/head.
Finishing Touches
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Actionable comments posted: 1
Fix comments: Fix CodeRabbit comments on this PR
Prompt to fix all issues
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Inline comments:
Review comments at @lib/msf/base/sessions/windows_escaping.rb:
- Around line 76-82: Reject arguments containing carriage returns or newlines in
the Windows branch of SingleCommandShell#to_cmd before they reach the escaping
flow that builds escaped_cmd_and_args. Raise an ArgumentError rather than
stripping or otherwise changing the argument; leave non-Windows handling
unchanged.
After applying the fix, consider running `coderabbit review --agent` for local
review. Visit https://docs.coderabbit.ai/cli?utm_source=ghpr
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cmd.exe splits its input into separate commands at a carriage return or
line feed before it applies quoting, so a line break embedded in an
argument cannot be neutralised by quoting and would start a second
command on a Windows command-shell session. Quoting (as first attempted
here) does not close this path.
Reject arguments containing "\r" or "\n" in the Windows to_cmd instead,
raising ArgumentError rather than emitting an unsafe command line. The
Unix path keeps quoting, which is sufficient there. The Windows
argv_to_commandline path is unchanged: it targets CreateProcess, which
does not treat line breaks as command separators.
Update the Windows spec to expect the rejection.
Verified: bundle exec rspec on both session specs passes (30 examples,
0 failures).
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Description
create_processescapes each argument with the session'sto_cmdbefore the command reaches a shell, which is what makes passing an argument array safe against command injection. However, the Unixescape_argquote_requiringlist and the Windowscmd.exeto_cmdlist did not include newline, carriage return or tab.As a result, an argument such as
example.com\nidpassed through unquoted, and a POSIX shell (orcmd.exe) treats the bare newline as a command separator — so the second token runs as its own command. This weakens the injection guarantee for everycreate_processcaller whose argument can contain a newline.For Unix this adds
"\n","\r"and"\t"to thequote_requiringlist; a POSIX shell treats a newline inside single quotes as a literal, so quoting is sufficient.For Windows this is not sufficient:
cmd.exesplits its input into commands at a carriage return or line feed before it applies quoting, so a quoted newline still starts a second command on a command-shell session. The Windowsto_cmdtherefore rejects arguments containing\r/\nwithArgumentErrorrather than emitting an unsafe command line. (Thanks to CodeRabbit for catching that quoting is not enough oncmd.exe.)The Windows
argv_to_commandlinepath is intentionally left unchanged: it targetsCreateProcessviaCommandLineToArgvW, which parses an argv and does not treat line breaks as command separators, so there is no shell to inject into there.Scope: framework escaping helpers only; no module changes.
Surfaced by CodeRabbit on #22140 (where it is correctly out of scope for that module, since the fix belongs in the shared helper).
AI tools used: Claude Code (assisted with the analysis, the fix, and the spec additions).
Verification
bundle exec rspec spec/lib/msf/base/sessions/command_shell_unix_spec.rb spec/lib/msf/base/sessions/command_shell_windows_spec.rbpasses, including the new newline/CR/tab cases.bundle exec rubocop lib/msf/base/sessions/unix_escaping.rb lib/msf/base/sessions/windows_escaping.rbadds no new offenses.Results
bundle exec rspecon both session specs:30 examples, 0 failures, including the new newline/CR/tab cases.Live before/after on Linux, same
cmd/unix/reverse_bashsession and same payload, driving the session's realto_cmd+shell_command_token(the shell pathcreate_processuses). The argument isx\n{touch,/tmp/pwn_nl}— a newline with no other quote-triggering character, using brace expansion so no space is needed:The Windows
cmd.exepath rejects line breaks and is covered by a unit spec assertingArgumentError(no Windows target available for a live run); theargv_to_commandlinepath is unchanged by design.