CVE-2026-35042 — fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation)
fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.1.0 and earlier, fast-jwt does not validate the crit (Critical) Header Parameter defined in RFC 7515 §4.1.11. Wh…
Published: 2026-04-06 · CVSS: 7.5 · CVSS 3.1
fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.1.0 and earlier, fast-jwt does not validate the crit (Critical) Header Parameter defined in RFC 7515 §4.1.11. When a JWS token contains a crit array listing extensions that fast-jwt does not understand, the library accepts the token instead of rejecting it. This violates the MUST requirement in the RFC.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7