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Medium

Symfony: Mailomat Mailer Webhook Parser Reads the HMAC Algorithm from the Request: Signature Algorithm Downgrade

  • Disclosed: 15.06.2026
  • Updated: 11.10.2026 10:22

Description

Symfony\Component\Mailer\Bridge\Mailomat\Webhook\MailomatRequestParser::validateSignature() parses the X-MOM-Webhook-Signature request header as algo=signature and passes the wire-supplied $algo directly to hash_hmac() when verifying the request against the configured webhook secret. The request therefore selects the HMAC primitive used to authenticate it.

PHP's hash_hmac() enforces only that the chosen algorithm is HMAC-compatible. That set still includes primitives with known cryptanalysis (md4, md5, ripemd128, tiger128,3, … — e.g. existential forgery of HMAC-MD4, Contini & Yin, ASIACRYPT 2006). This is the canonical algorithm-confusion shape, analogous to JWT alg=none / alg=HS256 downgrades: any future cryptographic weakness in any HMAC primitive PHP exposes becomes immediately exploitable against a Mailomat webhook receiver, the moment an attacker is in a position to compute a signature for that primitive, without a code change on the Symfony side.

Mailomat's documented webhook security pins SHA-256; the parser did not.

Resolution

MailomatRequestParser::validateSignature() now requires the signature header to be of the form sha256=<hex> and verifies the signature with HMAC-SHA256 keyed by the configured secret using a constant-time comparison. Any other algorithm declared on the wire (including the HMAC primitives PHP would otherwise accept) is rejected.

The patch for this issue is available here for branch 7.4 (and forward-ported to 8.0 and 8.1).

Credits

Symfony would like to thank Omar Alshammari, Essam Alanazi and Alwaleed Alshammari for reporting the issue and Nicolas Grekas for providing the fix.

Affected software

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PlatformPackageVulnerable versionsFixed in
Composer package symfony/mailomat-mailer >= 7.2.0, < 7.4.13, >= 8.0.0, < 8.0.13 7.4.13, 8.0.13
Composer package symfony/symfony >= 7.2.0, < 7.4.13, >= 8.0.0, < 8.0.13 7.4.13, 8.0.13

References

CVSS score -
Weakness (CWE)
CWE-347, CWE-757
Platform
Composer
Package
symfony/mailomat-mailer, symfony/symfony
Disclosed
15.06.2026
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-rrj9-5q2j-4gvr - CC BY 4.0

Vulnerability history: symfony/symfony

All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (100) in the archive
Total entries
100
First → latest
11.2019 06.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • Critical 8
  • High 28
  • Medium 51
  • Low 13

Disclosures per year

Severity:
  1. Symfony: Mailomat Mailer Webhook Parser Reads the HMAC Algorithm from the Request: Signature Algorithm Downgrade this entry
    Medium CVE-2026-48747 >= 7.2.0, < 7.4.13, >= 8.0.0, < 8.0.13 7.4.13, 8.0.13
  2. Symfony: Security Firewall Bypass via failure_forward Subrequest: Unauthenticated Access to access_control-Protected GET Routes
    High CVE-2026-48489 < 5.4.53, >= 6.0.0, < 6.4.41, >= 7.0.0, < 7.4.13, >= 8.0.0, < 8.0.13 5.4.53, 6.4.41, 7.4.13, 8.0.13
  3. Symfony has Unauthenticated PHP Object Deserialization in MonologBridge server:log Listener
    High CVE-2026-45077 < 5.4.52, >= 6.0.0, < 6.4.40, >= 7.0.0, < 7.4.12, >= 8.0.0, < 8.0.12 5.4.52, 6.4.40, 7.4.12, 8.0.12
  4. Symfony's HEAD Request Bypasses methods: ['GET'] Filter in #[IsGranted] / #[IsSignatureValid] / #[IsCsrfTokenValid]
    High CVE-2026-45075 >= 7.4.0, < 7.4.12, >= 8.0.0, < 8.0.12 7.4.12, 8.0.12
  5. Symfony has Email Header / SMTP Command Injection via CRLF in Symfony\Component\Mime\Address
    High CVE-2026-45067 < 5.4.52, >= 6.0.0, < 6.4.40, >= 7.0.0, < 7.4.12, >= 8.0.0, < 8.0.12 5.4.52, 6.4.40, 7.4.12, 8.0.12
  6. Symfony Vulnerable to Identity Spoofing via Unanchored DN Regex in X509Authenticator
    High CVE-2026-45063 < 5.4.52, >= 6.0.0-BETA1, < 6.4.40, >= 7.0.0-BETA1, < 7.4.12, >= 8.0.0-BETA1, < 8.0.12 5.4.52, 6.4.40, 7.4.12, 8.0.12
  7. Symfony's incorrect parsing of PATH_INFO can lead to limited authorization bypass
    High · 7.3 CVE-2025-64500 >= 2.0.0, < 5.4.50, >= 6.0.0, < 6.4.29, >= 7.0.0, < 7.3.7 5.4.50, 6.4.29, 7.3.7
  8. Symfony vulnerable to command execution hijack on Windows with Process class
    High · 8.4 CVE-2024-51736 < 5.4.46, >= 6.0.0, < 6.4.14, >= 7.0.0, < 7.1.7 5.4.46, 6.4.14, 7.1.7
  9. Symfony Cross-Site Request Forgery vulnerability in the Web Profiler
    High · 8.1 CVE-2014-6072 >= 2.0.0, < 2.3.19, >= 2.4.0, < 2.4.9, >= 2.5.0, < 2.5.4 2.3.19, 2.4.9, 2.5.4
  10. Symfony XML Entity Expansion security vulnerability
    High · 7.5 ghsa-q2gc-gg3x-7942 >= 2.0.0, < 2.0.17 2.0.17
  11. Symfony XML decoding attack vector through external entities
    Critical · 9.8 ghsa-mmcv-fvq8-r9x3 >= 2.0.0, < 2.0.11 2.0.11
  12. Symfony allows direct access of ESI URLs behind a trusted proxy
    High · 7.5 CVE-2014-5245 >= 2.0.0, < 2.3.19, >= 2.4.0, < 2.4.9, >= 2.5.0, < 2.5.4 2.3.19, 2.4.9, 2.5.4
  13. Symfony vulnerable to denial of service via a malicious HTTP Host header
    High · 7.5 CVE-2014-5244 >= 2.0.0, < 2.3.19, >= 2.4.0, < 2.4.9, >= 2.5.0, < 2.5.4 2.3.19, 2.4.9, 2.5.4
  14. Code injection in the way Symfony implements translation caching in FrameworkBundle
    High · 7.5 CVE-2014-4931 >= 2.0.0, < 2.3.19, >= 2.4.0, < 2.4.9, >= 2.5.0, < 2.5.4 2.3.19, 2.4.9, 2.5.4
  15. Symfony Incorrect Access Control
    Critical · 9.8 CVE-2017-11365 >= 2.7.30, < 2.7.32, >= 2.8.23, < 2.8.25, >= 3.2.10, < 3.2.12, >= 3.3.3, < 3.3.5 2.7.32, 2.8.25, 3.2.12, 3.3.5
  16. Symphony Denial of Service Via Overlong Usernames
    High · 7.5 CVE-2016-4423 >= 2.3.0, < 2.3.41, >= 2.4.0, < 2.7.13, >= 2.8.0, < 2.8.6, >= 3.0.0, < 3.0.6 2.3.41, 2.7.13, 2.8.6, 3.0.6
  17. Symfony Cryptographic Vulnerability
    High · 7.5 CVE-2016-1902 >= 2.3.0, < 2.3.37, >= 2.4.0, < 2.6.13, >= 2.7.0, < 2.7.9 2.3.37, 2.6.13, 2.7.9
  18. Symfony Vulnerable to Timing Attack
    High CVE-2015-8125 >= 2.3.0, < 2.3.35, >= 2.7.0, < 2.7.7, >= 2.4.0, < 2.6.12 2.3.35, 2.7.7, 2.6.12
  19. Symphony Vulnerable to PHP Code Injection via YAML Parsing
    High CVE-2013-1348 >= 2.0.0, < 2.0.22 2.0.22
  20. Symfony Arbitrary PHP code Execution
    High CVE-2013-1397 >= 2.2.0-BETA1, < 2.2.0-BETA2, >= 2.0.0, < 2.0.22, >= 2.1.0, < 2.1.7 2.2.0-BETA2, 2.0.22, 2.1.7
  21. Symfony Authentication Bypass
    Critical · 9.8 CVE-2018-11407 >= 2.8.0, < 2.8.37, >= 3.0.0, < 3.3.17, >= 3.4.0, < 3.4.7, >= 4.0.0, < 4.0.7 2.8.37, 3.3.17, 3.4.7, 4.0.7
  22. Symfony Authentication Bypass
    Critical · 9.8 CVE-2016-2403 >= 2.8.0, < 2.8.6, >= 3.0.0, < 3.0.6 2.8.6, 3.0.6
  23. Symfony Host Header Injection
    High · 7.2 CVE-2018-14774 >= 2.7.0, < 2.7.49, >= 2.8.0, < 2.8.44, >= 3.3.0, < 3.3.18, >= 3.4.0, < 3.4.14, >= 4.0.0, < 4.0.14, >= 4.1.0, < 4.1.3 2.7.49, 2.8.44, 3.3.18, 3.4.14, 4.0.14, 4.1.3
  24. Symfony Session Fixation Vulnerability
    High · 8.1 CVE-2018-11385 >= 2.7.0, < 2.7.48, >= 2.8.0, < 2.8.41, >= 3.0.0, < 3.3.17, >= 3.4.0, < 3.4.11, >= 4.0.0, < 4.0.11 2.7.48, 2.8.41, 3.3.17, 3.4.11, 4.0.11
  25. Symfony Directory Traversal
    High · 7.5 CVE-2017-16654 >= 2.7.0, < 2.7.38, >= 2.8.0, < 2.8.31, >= 3.0.0, < 3.2.14, >= 3.3.0, < 3.3.13 2.7.38, 2.8.31, 3.2.14, 3.3.13
  26. Symfony CSRF Token Fixation
    High · 8.8 CVE-2018-11406 >= 2.7.0, < 2.7.48, >= 2.8.0, < 2.8.41, >= 3.0.0, < 3.3.17, >= 3.4.0, < 3.4.11, >= 4.0.0, < 4.0.11 2.7.48, 2.8.41, 3.3.17, 3.4.11, 4.0.11
  27. Symfony collectionCascaded and collectionCascadedDeeply fields security bypass
    High · 8.1 CVE-2013-4751 >= 2.0.0, < 2.0.24, >= 2.1.0, < 2.1.12, >= 2.2.0, < 2.2.5, >= 2.3.0, < 2.3.3 2.0.24, 2.1.12, 2.2.5, 2.3.3
  28. Symfony Http-Kernel has non-constant time comparison in UriSigner
    High · 8.1 CVE-2019-18887 >= 2.2.0, < 2.8.52, >= 3.0.0, < 3.4.35, >= 4.0.0, < 4.2.12, >= 4.3.0, < 4.3.8 2.8.52, 3.4.35, 4.2.12, 4.3.8
  29. RCE in Symfony
    High · 8.0 CVE-2020-15094 >= 4.3.0, < 4.4.13, >= 5.0.0, < 5.1.5 4.4.13, 5.1.5
  30. Firewall configured with unanimous strategy was not actually unanimous in Symfony
    High · 7.6 CVE-2020-5275 >= 4.4.0, < 4.4.7, >= 5.0.0, < 5.0.7 4.4.7, 5.0.7
  31. Improper authentication in Symfony
    High · 7.5 CVE-2019-10911 >= 2.7.0, < 2.7.51, >= 2.8.0, < 2.8.50, >= 3.0.0, < 3.4.26, >= 4.0.0, < 4.1.12, >= 4.2.0, < 4.2.7 2.7.51, 2.8.50, 3.4.26, 4.1.12, 4.2.7
  32. Deserialization of untrusted data in Symfony
    High · 7.1 CVE-2019-10912 >= 2.8.0, < 2.8.50, >= 3.0.0, < 3.4.26, >= 4.0.0, < 4.1.12, >= 4.2.0, < 4.2.7 2.8.50, 3.4.26, 4.1.12, 4.2.7
  33. Improper Input Validation in Symfony
    Critical · 9.8 CVE-2019-11325 >= 4.2.0, < 4.2.12, >= 4.3.0, < 4.3.8 4.2.12, 4.3.8
  34. Invalid HTTP method overrides allow possible XSS or other attacks in Symfony
    Critical · 9.8 CVE-2019-10913 >= 2.7.0, < 2.7.51, >= 2.8.0, < 2.8.50, >= 3.0.0, < 3.4.26, >= 4.0.0, < 4.1.12, >= 4.2.0, < 4.2.7 2.7.51, 2.8.50, 3.4.26, 4.1.12, 4.2.7
  35. Argument injection in a MimeTypeGuesser in Symfony
    High · 7.5 CVE-2019-18888 >= 2.0.0, < 2.8.52, >= 3.0.0, < 3.4.35, >= 4.0.0, < 4.2.12, >= 4.3.0, < 4.3.8 2.8.52, 3.4.35, 4.2.12, 4.3.8
  36. Symfony Unsafe Cache Serialization Could Enable RCE
    Critical · 9.8 CVE-2019-18889 >= 3.1.0, < 3.4.35, >= 4.0.0, < 4.2.12, >= 4.3.0, < 4.3.8 3.4.35, 4.2.12, 4.3.8
  37. Symfony Service IDs Allow Injection
    Critical · 9.8 CVE-2019-10910 >= 2.7.0, < 2.7.51, >= 2.8.0, < 2.8.50, >= 3.0.0, < 3.4.26, >= 4.0.0, < 4.1.12, >= 4.2.0, < 4.2.7 2.7.51, 2.8.50, 3.4.26, 4.1.12, 4.2.7

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