fix: symlink sandbox bypass in isWithinPath (security) — v0.12.10#74
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The Pi extension's tool-call sandbox used lexical path comparison (resolve()) without resolving symlinks. A sub-agent could create a symlink inside .codecarto/ pointing to a file outside the allowed root (e.g. ~/.ssh/id_rsa) and write through it -- the isWithinPath guard would pass because it only checked the lexical path, not the resolved target. Fix: added isWithinPathResolved which uses realpath before comparison. Updated the Pi tool_call hook to use isWithinPathResolved instead of isWithinPath. The MCP server was not affected (it does not use isWithinPath). Regression tests: - Documents the vulnerability (lexical check returns true for symlink) - Verifies the fix (resolved check returns false for symlink) - Verifies legitimate paths still pass - Verifies the root itself passes Discovered during the v0.12.9 self-analysis case study, independently confirmed via reproduction, and fixed with regression coverage. 268/268 tests pass (264 original + 4 new).
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Security fix
The Pi extension's tool-call sandbox used lexical path comparison () without resolving symlinks. A sub-agent could create a symlink inside pointing to a file outside the allowed root and write through it — the guard would pass because it only checked the lexical path.
Fix
Discovery
Found during the v0.12.9 self-analysis case study. The semantic defect scan (Pass 4: Security & Trust) identified it. Independent reproduction confirmed: a symlink inside an allowed directory pointing outside passes the lexical check but fails the resolved check.
Validation