CVE-2026-63405: AnyCable Pusher REST API Does Not Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5p54-whvp-x327",
  "modified" : "2026-09-18T17:16:25Z",
  "published" : "2026-09-18T17:16:25Z",
  "aliases" : [ "CVE-2026-63405" ],
  "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/<app_id>/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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/anycable/anycable"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.6.15"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.6.14"
    }
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-345" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-18T17:16:25Z",
    "nvd_published_at" : null
  }
}