`browse/src/domain-skill-commands.ts:140` (handleSave) writes
`classifier_score: 0` with the comment "L4 deferred to load-time / sidebar-agent
fills this in on first prompt-injection load." But CLAUDE.md "Sidebar
architecture" documents that sidebar-agent.ts was ripped, and grep for
recordSkillUse + classifierFlagged callers across browse/src/ returns zero hits
outside the module under test.
Net effect: every quarantined skill that survives three benign uses without
flag (`recordSkillUse(... , classifierFlagged: false)` x3) auto-promotes to
`active` and lands in prompt context wrapped as UNTRUSTED on every subsequent
visit to that host. The L4 score that was supposed to gate the promotion was
never written — the production save path puts 0 on disk and nothing later
updates it.
Threat model: a domain-skill body authored by an agent under the influence of
a poisoned page (the new `gstackInjectToTerminal` PTY path runs no L1-L3
either) would lose its auto-promote barrier after three uses. The exploit
isn't single-step but the bar is exactly N=3 prompt-injection-shaped uses on
a hostile page, which is well within reach.
Fix adds a single condition to the auto-promote gate in `recordSkillUse`:
if (state === 'quarantined' && useCount >= PROMOTE_THRESHOLD &&
flagCount === 0 && current.classifier_score > 0) {
state = 'active';
}
`classifier_score` is set once at writeSkill and never updated. Production
saves it as 0 (handleSave), so the gate stays closed; existing tests that
explicitly pass `classifierScore: 0.1` still auto-promote (the auto-promote
path is preserved for the day L4 is rewired).
Manual promotion via `domain-skill promote-to-global` is unaffected (it goes
through `promoteToGlobal` which has its own state-machine guard at line 337+).
Test: new regression case `does NOT auto-promote when classifier_score is 0
(production handleSave shape)` plants a skill with classifierScore=0 (matches
domain-skill-commands.ts:140), runs three uses without flag, asserts the skill
stays quarantined and readSkill returns null. Negative control: revert the
patch, the test fails with `Received: "active"`. With the patch: 15/15 pass.
`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