{"id":"CVE-2026-47074","aliases":["EEF-CVE-2026-47074","GHSA-8jgf-23q5-x7xx"],"url":"https://o3.security/vulnerability/CVE-2026-47074","summary":"ex_aws_sns SigningCertURL not validated in verify_message/1","details":"### Summary\n\n`ExAws.SNS.verify_message/1` fetches the signing certificate from the `SigningCertURL` field of the incoming SNS message without validating that the URL uses HTTPS or that its host is an AWS-owned SNS certificate domain. An unauthenticated attacker who can POST to any endpoint that calls `verify_message/1` can supply an attacker-controlled `SigningCertURL`, sign a forged SNS message with their own RSA key, and cause the function to return `:ok`, completely bypassing SNS signature verification.\n\n### Details\n\nIn `lib/ex_aws/sns.ex` (lines 475–483), `verify_message/1` performs three checks: `validate_message_params/1` (confirms required fields are present), `validate_signature_version/1` (confirms `SignatureVersion == \"1\"`), then signature verification. The signature step calls `ExAws.SNS.PublicKeyCache.get(message[\"SigningCertURL\"])` and passes the result to `:public_key.verify/4`.\n\nNeither `validate_message_params/1` nor any other step checks that `SigningCertURL` is an HTTPS URL or that the hostname matches the expected pattern (e.g. `sns.<region>.amazonaws.com`). `PublicKeyCache.get/1` in `lib/ex_aws/sns/public_key_cache.ex` fetches whatever URL is provided and caches the certificate. The RSA signature then verifies against the attacker's own public key, and `verify_message/1` returns `:ok`.\n\n### PoC\n\n1. Generate an RSA keypair and host the DER/PEM public certificate at any URL reachable from the target server (e.g. `http://attacker.example/cert.pem`).\n2. Build a forged `Notification` payload with an arbitrary `TopicArn` and `Message`, compute the canonical string-to-sign per the SNS spec, and sign it with the attacker private key.\n3. Set `SigningCertURL` to the attacker URL and `Signature` to the base64-encoded signature.\n4. POST the forged payload to any SNS webhook endpoint that calls `ExAws.SNS.verify_message/1`.\n5. The function returns `:ok`; the application treats the message as authentic.\n\n### Configurations\n\nThe application must expose an HTTP endpoint that calls `ExAws.SNS.verify_message/1` on incoming request bodies (the standard SNS webhook pattern).\n\n### Impact\n\nComplete SNS signature authentication bypass. Affects `ex_aws_sns` from 2.0.1 through 2.3.4. Consequences include spoofing arbitrary `Notification` payloads, auto-confirming attacker-controlled `SubscribeURL` values to hijack topic delivery, and spoofing `UnsubscribeConfirmation` to disrupt legitimate subscriptions. No authentication or special configuration on the attacker side is required. CVSS v4.0: **8.7 (HIGH)**.\n\n## Resources\n\n* Introduction commit: https://github.com/ex-aws/ex_aws_sns/commit/a7ec21880943f4dac1d59bda557db0ffcd2b61fa\n* Patch commit: https://github.com/ex-aws/ex_aws_sns/commit/1853d280b152d10384a1e21a22cf22152a60be48","published":"2026-05-28T09:05:54.815Z","modified":"2026-10-21T02:58:13.977716048Z","cvss":null,"epss":{"score":0.00226,"percentile":0.13414,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Hex","name":"ex_aws_sns","fixedVersion":"2.3.5"}],"fix":{"url":"https://github.com/ex-aws/ex_aws_sns/commit/1853d280b152d10384a1e21a22cf22152a60be48","label":"ex-aws/ex_aws_sns@1853d28"},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-47074.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://hex.pm"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-47074"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47074.json"},{"type":"ADVISORY","url":"https://github.com/ex-aws/ex_aws_sns/security/advisories/GHSA-8jgf-23q5-x7xx"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-47074"},{"type":"FIX","url":"https://github.com/ex-aws/ex_aws_sns/commit/1853d280b152d10384a1e21a22cf22152a60be48"},{"type":"PACKAGE","url":"https://github.com/ex-aws/ex_aws_sns"},{"type":"WEB","url":"https://github.com/benoitc/hackney/security/advisories/GHSA-jq4m-q6p2-8gwc"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:58:13.977716048Z"}}