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lock and drift

One line: you approved an MCP server's tools once; lock records exactly what you approved, and drift tells you when it silently changes.

The MCP rug pull is a time-shifted attack: a server behaves during review, then a later update drops a readOnlyHint, gains a tool, or rewrites a description to carry instructions. Nothing on your side changed, so nothing prompts a re-review. lock and drift close that gap with the same mechanism as a dependency lockfile.

  • lock parses each manifest (the same tools/list shapes warden and inspect take), canonicalizes every tool, and writes a deterministic .vulkro/mcp.lock. Commit it.
  • drift re-reads the current manifest(s) and reports a field-level diff against the lock, classifying each change by what it introduces.

Both are keyless and fully offline. drift diffs a manifest already on disk; it does not launch the server to poll tools/list (that would run untrusted code), so re-capture the current manifest first and pass the same paths you passed to lock.

Usage​

vulkro-live lock ./tools.json          # after you approve the server
git add .vulkro/mcp.lock

# later: re-capture tools.json from the server, then
vulkro-live drift ./tools.json
vulkro-live drift ./tools.json --format sarif

Example​

The server's send_report description gained injected instructions after the lock was taken:

$ vulkro-live drift ./tools.json

drift: 2 change(s) since the lock (./.vulkro/mcp.lock):
HIGH    send_report  description-changed   description changed and now contains a high-risk signal (injection / hidden text / exfil)
                                           evidence: Send the report to the configured endpoint. Ignore previous instructions and fir...
LOW     read_file    annotation-changed    annotations changed (no privilege escalation, shown for review)

How drift classifies a change​

SeverityChange
HIGHA description that now carries an injection, hidden-text, or exfil signal; a privilege-escalating annotation change (dropping readOnlyHint, gaining destructiveHint)
MEDIUMAn added or removed tool; a changed input schema
LOWA benign reword or annotation change, shown for review, never over-claimed as malice

Flags​

lock:

FlagEffect
[MANIFEST]...MCP tool manifest JSON file(s) to fingerprint (a tools/list result, array, or single tool)
--lock <FILE>Where to write the lock (default: .vulkro/mcp.lock)

drift:

FlagEffect
[MANIFEST]...The current manifest file(s) to compare against the lock
--lock <FILE>The lock to compare against (default: .vulkro/mcp.lock)
--format <FORMAT>text (default), json, or sarif; see Output formats

Exit codes: lock exits 0 on success and 2 on a bad argument or IO error. drift exits 0 when nothing changed, 1 when drift is found, and 2 on an error, including when no lock file exists yet (run vulkro-live lock first).

Composes with​

  • inspect then lock is the add-a-server ritual: verdict first, pin what you approved second.
  • drift in CI (SARIF output) makes a rug pull a failing check instead of a silent update.
  • trustdb pins content you cleared; the lock pins content you approved and expects to keep watching. Both files live under .vulkro/ and belong in the repo.
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