hook: refuse a quoted command string passed through a login shell - #508
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`sudo -i` starts the target user's login shell, and that shell parses the remaining arguments a second time. The quoting the first parse consumed is gone by then, so the command string is re-split and its first word becomes the whole command. A handoff script died this way in a user's terminal. Reproduced on a real host, one variable apart: `sudo -u demo -H bash -lc '<body>'` prints the body's output, and the same line with `-i` gives `bash: line 1: set: -c: invalid option`. Newlines are not the trigger, which is what the first reading of the failure got wrong. A multi-line body survives ssh and survives sudo without `-i`. Backtested over 37,015 real Bash commands: 6 hits, all the broken shape. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01KU2pPKob4MJ1NqjsfTNyYJ Change-Id: Iacc7d62317959adeb953d4fef0bc9dc222a37430
This was referenced Sep 12, 2026
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This was referenced Sep 12, 2026
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sudo -istarts the target user's login shell, and that shell parses theremaining arguments a second time. The quoting the first parse consumed is
gone by then, so the command string is re-split and its first word becomes
the whole command. A handoff script died this way in a user's terminal.
Reproduced on a real host, one variable apart:
sudo -u demo -H bash -lc '<body>'prints the body's output, and the same line with-igivesbash: line 1: set: -c: invalid option.Newlines are not the trigger, which is what the first reading of the
failure got wrong. A multi-line body survives ssh and survives sudo without
-i.Backtested over 37,015 real Bash commands: 6 hits, all the broken shape.
Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01KU2pPKob4MJ1NqjsfTNyYJ
Depends-On: #507
Note
Low Risk
Adds an optional PreToolUse gate on Bash commands with fail-open error handling; may block rare legitimate sudo -i + quoted -c patterns until rewritten.
Overview
Adds a new Claude PreToolUse (Bash) hook,
remote-payload-collapses, that blocks commands where a quoted command string is passed throughsudo -i,su -, orsu -l. The login shell re-parses arguments after the first parse consumed quoting, so the payload is re-split and often breaks (e.g.bash -lc '<body>'vs the same line with-i).Detection is text-only (
detect.collapse_risk): login-shell pattern, a carried interpreter (bash,-c, etc.), and quotes in the tail; heredocs are stripped so stdin/file patterns stay allowed. On match the hook exits 2 with remediation (drop-i, or scp + run by path); malformed JSON and detector errors fail open.install.shsymlinks the hook and mergesinstall_claude_hook.pyinto~/.claude/settings.json. README /docs/ecosystem.mddocument it; unit tests cover fire/silent fixtures and install wiring.Reviewed by Cursor Bugbot for commit d76e1e5. Bugbot is set up for automated code reviews on this repo. Configure here.