CVE-2026-3419 (GCVE-0-2026-3419)

Vulnerability from cvelistv5 – Published: 2026-03-06 17:50 – Updated: 2026-03-09 14:55
VLAI?
Title
Fastify's Missing End Anchor in "subtypeNameReg" Allows Malformed Content-Types to Pass Validation
Summary
Fastify incorrectly accepts malformed `Content-Type` headers containing trailing characters after the subtype token, in violation of RFC 9110 §8.3.1(https://httpwg.org/specs/rfc9110.html#field.content-type). For example, a request sent with Content-Type: application/json garbage passes validation and is processed normally, rather than being rejected with 415 Unsupported Media Type. When regex-based content-type parsers are in use (a documented Fastify feature), the malformed value is matched against registered parsers using the full string including the trailing garbage. This means a request with an invalid content-type may be routed to and processed by a parser it should never have reached. Impact: An attacker can send requests with RFC-invalid Content-Type headers that bypass validity checks, reach content-type parser matching, and be processed by the server. Requests that should be rejected at the validation stage are instead handled as if the content-type were valid. Workarounds: Deploy a WAF rule to protect against this Fix: The fix is available starting with v5.8.1.
Severity ?
5.3 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
CWE
  • CWE-185 - Incorrect Regular Expression
Assigner
References
Impacted products
Vendor Product Version
fastify fastify Affected: 5.7.2 , < 5.8.1 (semver)
Unaffected: 5.8.1 (semver)
Create a notification for this product.
Credits
Saad FELLAHI James Sumners Matteo Collina Ulises Gascón
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