engram: HTTP server CORS wildcard + auth-off-by-default enables CSRF graph exfiltration and persistent indirect prompt injection

Summary

The local HTTP server started by engram server (binding 127.0.0.1:7337 by default) was exposed to any browser origin with no authentication unless ENGRAM_API_TOKEN was explicitly set. Combined with Access-Control-Allow-Origin: * on every response and a body parser that did not require Content-Type: application/json, this allowed a malicious web page the developer visited to:

1. Exfiltrate the local knowledge graph via GET /query and GET /stats (function names, file layout, recorded decisions/mistakes).
2. Inject persistent prompt-injection payloads via POST /learn, which wrote mistake/decision nodes that were later surfaced as system-reminders to the user's AI coding agent on every future session and file edit.

Severity: High — confidentiality + persistent indirect prompt injection against the user's coding agent.

Affected versions

engramx >= 1.0.0, < 2.0.2 — any version that shipped the HTTP server.

Patched in

engramx@2.0.2

Workarounds (if you cannot upgrade)

• Do not run engram server or engram ui.
• If developers must, set ENGRAM_API_TOKEN to a long random value and terminate the server before browsing the web.

Remediation (applied in 2.0.2)

1. Fail-closed auth on every non-public route — Bearer header or HttpOnly cookie, constant-time comparison, 256-bit auto-generated token at ~/.engram/http-server.token (0600).
2. Wildcard CORS removed entirely; default is no CORS headers. Opt-in allowlist via ENGRAM_ALLOWED_ORIGINS.
3. Host + Origin validation — rejects DNS rebinding and Host spoofing.
4. Content-Type: application/json enforced on mutations — blocks the text/plain CSRF vector.
5. /ui?token= bootstrap with Sec-Fetch-Site gate — prevents cross-origin oracle probing.

Credit

Discovered and responsibly disclosed by @gabiudrescu in engram issue #7.