GHSA-8JGF-23Q5-X7XX

Vulnerability from github – Published: 2026-06-26 22:50 – Updated: 2026-06-30 17:16
VLAI
Summary
ex_aws_sns: Trusted-attacker `SigningCertURL` permits complete SNS signature bypass
Details

Summary

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.

Details

In 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.

Neither 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.

PoC

  1. 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).
  2. 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.
  3. Set SigningCertURL to the attacker URL and Signature to the base64-encoded signature.
  4. POST the forged payload to any SNS webhook endpoint that calls ExAws.SNS.verify_message/1.
  5. The function returns :ok; the application treats the message as authentic.

Configurations

The application must expose an HTTP endpoint that calls ExAws.SNS.verify_message/1 on incoming request bodies (the standard SNS webhook pattern).

Impact

Complete 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).

Resources

  • Introduction commit: https://github.com/ex-aws/ex_aws_sns/commit/a7ec21880943f4dac1d59bda557db0ffcd2b61fa
  • Patch commit: https://github.com/ex-aws/ex_aws_sns/commit/1853d280b152d10384a1e21a22cf22152a60be48
Severity
8.7 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Hex",
        "name": "ex_aws_sns"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.1"
            },
            {
              "fixed": "2.3.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-47074"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-295"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-26T22:50:27Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "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\u2013483), `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.\u003cregion\u003e.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\u0027s 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",
  "id": "GHSA-8jgf-23q5-x7xx",
  "modified": "2026-06-30T17:16:17Z",
  "published": "2026-06-26T22:50:27Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/benoitc/hackney/security/advisories/GHSA-jq4m-q6p2-8gwc"
    },
    {
      "type": "WEB",
      "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": "WEB",
      "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://osv.dev/vulnerability/EEF-CVE-2026-47074"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "ex_aws_sns: Trusted-attacker `SigningCertURL` permits complete SNS signature bypass"
}


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