fix(desktop): frame each tmux format record so a newline in a field cannot forge a pane by waleedlatif1 · Pull Request #8725 · simstudioai/sim

waleedlatif1 · 2026-10-07T05:37:45Z

Summary

tmux prints a newline inside a -F field as is. Suppose a pane's working directory (or its window title, or its command's name) holds a newline followed by separator-joined text, such as a + newline + user:0.0<~sim~>forged<~sim~>rm -rf<~sim~>home.
Its own record then ends early, and the rest reads as a whole pane of its own: any target, command and path. Meanwhile the real pane drops out of panes.
That lets a crafted directory name misattribute pane targets. The pane argument then sends input to, or closes, the wrong pane.
The fix, in two layers:
- Newlines are neutralised at the source. In the fields someone other than the user can set, tmux replaces each newline with <NL> itself (#{s/<newline>/<NL>/:…}). Those fields are the pane's directory, its command's name, and the window title a program sets with an escape sequence. A record is then always one line.
  - Session names stay as they are: users name their own sessions, and a record a newline would split is dropped by the frame.
- Each record is framed per call. Every -F read (list-clients, list-panes, and the active-pane lookup) wraps each record in a marker made fresh for that call, and only lines framed whole are read.
  - The marker is not a secret. On macOS ps shows any process's arguments, and on Linux /proc/<pid>/cmdline is world-readable. So the marker is a second line of defence for fields tmux prints raw, not the protection itself.
The separator comment now describes this model.
tmux output is decoded as a stream, so a character split across two chunks arrives whole.

Type of Change

Bug fix

Testing

Real tmux 2.9a and 3.4:
- Output captured verbatim for the forging directory: without neutralisation the forged rm -rf row is read; with it, the pane is one line and nothing is forged.
- listPanes returns nothing for the forging session, and a directory holding just a newline lists as one pane with <NL> in its path.
- activePane still resolves.
Unit tests, each failing when its guard is undone:
- a fake tmux that evaluates formats as tmux does lists a pane whose directory and title hold newlines as one pane;
- two calls are framed with different markers;
- a line framed at one end only is dropped, even when it has the right field count;
- a record framed by another call is dropped.

Checklist

Code follows project style guidelines
Self-reviewed my changes
Tests added/updated and passing
No new warnings introduced
I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

…annot forge a pane tmux prints a newline inside a `-F` field as is. A pane whose working directory (or window name, or session name) held a newline followed by separator-joined text ended its own record early and forged another: any target, command and path, while the real pane disappeared from `panes`. Every `-F` read (list-clients, list-panes, the active pane) now frames each record with a marker made fresh for that call, and only lines framed whole by it are read. Nobody outside the call knows the marker, so no field can forge a record, and the halves of a record a newline split are each dropped.

waleedlatif1 · 2026-10-07T05:37:51Z

@greptile

vercel · 2026-10-07T05:37:51Z

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waleedlatif1 · 2026-10-07T05:37:52Z

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cubic-dev-ai · 2026-10-07T05:37:57Z

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All reported issues were addressed across 2 files

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greptile-apps · 2026-10-07T05:42:00Z

Confidence Score: 5/5

[Medium risk] Fixes tmux pane parsing to prevent forged records from newlines.

The PR appears safe to merge; no new actionable issue was found.

What we checked:

Format text stays outside HTML: untrusted receives fixed field names. listPanes sends the resulting string to tmux as a format argument, not to browser HTML.

Summary

The PR frames tmux records with a fresh marker so text inside a field cannot be mistaken for another pane.

The latest changes replace newlines in pane titles, commands, and paths with <NL>.
runTmux now decodes UTF-8 across chunks without breaking characters.
Tests add captured output and checks for incomplete frames and newline-containing fields.
The earlier randomness-helper finding is fixed: framedFormat uses generateRandomHex(16).

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  Fields[Pane fields] --> Replace[Replace newlines with NL marker]
  Replace --> Frame[Add fresh frame around each record]
  Frame --> Tmux[tmux output]
  Tmux --> Check{Both frames and correct field count?}
  Check -->|Yes| Pane[Return pane]
  Check -->|No| Drop[Drop line]

_{Reviews (3) · Last reviewed commit: "fix(desktop): neutralise newlines at the..." · Reviewed by Greptile}

waleedlatif1 · 2026-10-07T05:50:03Z

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waleedlatif1 · 2026-10-07T05:50:05Z

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cubic-dev-ai · 2026-10-07T05:50:12Z

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cubic-dev-ai

No issues found across 2 files

Confidence score: 5/5

Automated review surfaced no issues in the provided summaries.
No files require special attention.

_{Turn on auto-fix | Re-trigger cubic}

… can set The per-call frame is not a secret: on macOS `ps` shows any process's arguments, and on Linux `/proc/<pid>/cmdline` is world-readable, so someone who owns the directory a pane sits in can read the frame and rename the directory before tmux reads it. tmux now replaces each newline with `<NL>` itself (`#{s/\n/<NL>/:…}`) in the fields someone other than the user can set: the pane's directory, its command, and the window title a program sets. A record is then one line, and the frame stays as a second line of defence. tmux output is also decoded as a stream, so a character split across two chunks arrives whole.

waleedlatif1 · 2026-10-07T06:22:23Z

@greptile

waleedlatif1 · 2026-10-07T06:22:24Z

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cubic-dev-ai · 2026-10-07T06:22:31Z

@cubic-dev-ai review this PR

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cubic-dev-ai

No issues found across 2 files

Confidence score: 5/5

Automated review surfaced no issues in the provided summaries.
No files require special attention.

_{Turn on auto-fix | Re-trigger cubic}

cubic-dev-ai Bot reviewed Oct 7, 2026

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Comment thread apps/desktop/src/main/terminal/tmux.ts Outdated

greptile-apps Bot reviewed Oct 7, 2026

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Comment thread apps/desktop/src/main/terminal/tmux.ts Outdated

fix(desktop): make the tmux format frame with the shared random helper

b1fed2e

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waleedlatif1 merged commit 566cea6 into staging Oct 7, 2026
36 of 37 checks passed

waleedlatif1 deleted the fix/desktop-tmux-format-framing branch October 7, 2026 07:15

This was referenced Oct 7, 2026

test(desktop): stop the agent's terminal commands in the real app, with real shells and real tmux #8733

Merged

refactor(desktop): one forward-only state per recorded tmux run, and one check for a delivered result #8737

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