{"id":"GHSA-5p54-whvp-x327","summary":"AnyCable: Pusher REST API Does Not Verify Request Body MD5 Enabling Signed-Request Replay with Arbitrary Body","details":"### Summary\nThe Pusher-compatible REST API includes `body_md5` in the HMAC signature string but never computes or verifies the MD5 of the received HTTP body, allowing anyone who observes a signed request to replay it with an entirely different body.\n\n### Details\nIn `pusher/http.go`, the `Handler` function extracts `body_md5` from the URL query string (line 169) and includes it verbatim in `stringToSign` (line 175). It then verifies `HMAC(stringToSign, secret) == auth_signature`. After verification succeeds, `handleEvents` reads and parses `r.Body` (lines 201-212) without ever computing `md5(body)` and comparing it against the `body_md5` that was signed. The Pusher protocol specification explicitly requires the server to verify this digest to prevent body-substitution attacks. There is also no `auth_timestamp` staleness check, so replays are valid indefinitely.\n\n### PoC\n1. Capture a legitimate signed POST to `/apps/\u003capp_id\u003e/events?auth_key=K&auth_timestamp=T&auth_version=1.0&body_md5=LEGIT_MD5&auth_signature=SIG` carrying body `{\"name\":\"safe-event\",\"channel\":\"ch\",\"data\":\"...\"}` (e.g., from TLS-terminating load-balancer logs).\n2. Send a new request with the same query string parameters but a different body:\n   `{\"name\":\"injected-event\",\"channel\":\"admin\",\"data\":\"malicious-payload\"}`\n3. The server accepts the request (HMAC over `stringToSign` matches the original) and broadcasts the injected event to all subscribers of `admin`.\n\n### Impact\nAn attacker who can read any single signed Pusher API request (from logs, a shared proxy, or a network tap) can broadcast arbitrary events to any channel indefinitely, potentially forging server-side events, corrupting application state, or delivering phishing messages to WebSocket clients.\n\n### Fix\nAfter reading `r.Body`, compute `hex(md5(body))` and compare it to the `body_md5` query parameter using a constant-time comparison before proceeding. Additionally, reject requests whose `auth_timestamp` is more than 600 seconds from the current time.","aliases":["CVE-2026-63405","GO-2026-6516"],"modified":"2026-09-28T17:10:52.635822676Z","published":"2026-09-18T17:16:25Z","database_specific":{"cwe_ids":["CWE-345"],"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2026-09-18T17:16:25Z","nvd_published_at":null},"references":[{"type":"WEB","url":"https://github.com/anycable/anycable/security/advisories/GHSA-5p54-whvp-x327"},{"type":"WEB","url":"https://github.com/anycable/anycable/commit/d2cbadec792f038f4695c84a65c0d957b0fde72c"},{"type":"PACKAGE","url":"https://github.com/anycable/anycable"},{"type":"WEB","url":"https://github.com/anycable/anycable/releases/tag/v1.6.15"}],"affected":[{"package":{"name":"github.com/anycable/anycable","ecosystem":"Go","purl":"pkg:golang/github.com/anycable/anycable"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.6.15"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 1.6.14","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-5p54-whvp-x327/GHSA-5p54-whvp-x327.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N"}]}