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fix(mcp): make session-marker symlink resistance work on Windows #337

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Merged
colbymchenry merged 1 commit into from
May 22, 2026
Merged

fix(mcp): make session-marker symlink resistance work on Windows #337

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11 changes: 11 additions & 0 deletions src/mcp/tools.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@ import {
constants as fsConstants,
closeSync,
existsSync,
lstatSync,
openSync,
readFileSync,
writeSync,
Expand Down Expand Up @@ -224,6 +225,16 @@ function markSessionConsulted(sessionId: string): void {
try {
const hash = createHash('md5').update(sessionId).digest('hex').slice(0, 16);
const markerPath = join(tmpdir(), `codegraph-consulted-${hash}`);
// Refuse to follow a pre-planted symlink at the marker path (CWE-59).
// O_NOFOLLOW (below) is the atomic, TOCTOU-free guard on POSIX, but it is
// `undefined` on Windows (libuv ignores it), so the bitwise-OR silently
// drops it and openSync would follow the link. This lstat check closes that
// gap cross-platform; ENOENT (path is free) falls through to create it.
try {
if (lstatSync(markerPath).isSymbolicLink()) return;
} catch {
// No existing entry (or stat failed) — nothing to refuse; proceed.
}
// O_NOFOLLOW makes openSync throw ELOOP if markerPath is already a symlink.
// O_CREAT + O_TRUNC keep the original "create-or-overwrite" semantics, and
// mode 0o600 prevents readback by other local users (the marker payload is
Expand Down