fix(mcp): make session-marker symlink resistance work on Windows#337
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O_NOFOLLOW is undefined on Windows (libuv ignores it), so the bitwise-OR silently dropped it and markSessionConsulted would follow a pre-planted symlink at the tmp marker path — the CWE-59 gap #280 closed on POSIX but not Windows. Add a cross-platform lstatSync isSymbolicLink() refuse-check before openSync (O_NOFOLLOW stays as the atomic, TOCTOU-free guard on POSIX). The existing Session-marker-symlink-resistance test now passes on Windows. Refs #280 Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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What
markSessionConsulted(the/tmpsession-consulted marker write) relied onO_NOFOLLOWto refuse a pre-planted symlink at the marker path — the CWE-59 protection added in #280. Butfs.constants.O_NOFOLLOWisundefinedon Windows (libuv ignores it), soO_WRONLY | O_CREAT | O_TRUNC | undefinedsilently drops the flag andopenSyncfollows the symlink, overwriting the target.Fix
Add a cross-platform
lstatSync(markerPath).isSymbolicLink()refuse-check beforeopenSync.O_NOFOLLOWstays as the atomic, TOCTOU-free guard on POSIX; the lstat check covers Windows (small lstat→open TOCTOU window, acceptable for a benign marker).Validation
security.test.tsnow fully green (37 passed, 2 skipped). TheSession marker symlink resistance > does not follow a pre-planted symlinktest — which failed on Windows before this change — now passes.Found while validating #327/#230 on a Windows VM. Refs #280.
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