`bin/gstack-memory-ingest.ts:632-643` ran `execSync(\`git -C ${JSON.stringify(cwd)}
remote get-url origin 2>/dev/null\`, ...)`. JSON.stringify escapes `"` and `\`
but not `$` or backticks, so a `cwd` of `"$(touch /tmp/marker)"` survived JSON
quoting and detonated under /bin/sh's command-substitution-inside-double-quotes.
`cwd` originates from transcript JSONL records under
`~/.claude/projects/<encoded-cwd>/<uuid>.jsonl` and
`~/.codex/sessions/YYYY/MM/DD/rollout-*.jsonl`. The walker grabs the first
`.cwd` it sees per session. That's an untrusted surface in the gstack threat
model — the L1-L6 sidebar security stack exists exactly because agent
transcripts can carry attacker-influenced text. Two pivots above the local
same-uid bar: (a) prompt-injection appending `cwd="$(...)"` to the active
session log turns the next /sync-gbrain run into RCE under the user's uid;
(b) cross-machine transcript share (a colleague's `.claude/projects` snippet
untar'd into HOME, a documented gbrain dogfooding shape) → RCE on first sync.
Fix swaps the one execSync for `execFileSync("git", ["-C", cwd, "remote",
"get-url", "origin"], ...)`. No shell, argv passed directly to git. The same
module already uses execFileSync for `gbrainAvailable()` (line 762 pre-patch)
and `gbrainPutPage()` (line 816 pre-patch) — this single execSync was the
outlier.
Test: `gstack-memory-ingest security: untrusted cwd cannot trigger shell
substitution` plants a Claude-Code-shaped JSONL with cwd=`$(touch <marker>)`
and asserts the marker file is not created after `--incremental --quiet`.
Negative control: with the patch reverted, the test fails (marker created);
with the patch applied, it passes (18/18 in test/gstack-memory-ingest.test.ts).
gus
d173a651a0