CVE-2021-41106: File reference keys leads to incorrect hashes on HMAC algorithms

Severity: low (CVSS 3.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-09-28 · updated 2026-06-17
Weakness: CWE-345

Description

JWT is a library to work with JSON Web Token and JSON Web Signature. Prior to versions 3.4.6, 4.0.4, and 4.1.5, users of HMAC-based algorithms (HS256, HS384, and HS512) combined with `Lcobucci\JWT\Signer\Key\LocalFileReference` as key are having their tokens issued/validated using the file path as hashing key - instead of the contents. The HMAC hashing functions take any string as input and, since users can issue and validate tokens, users are lead to believe that everything works properly. Versions 3.4.6, 4.0.4, and 4.1.5 have been patched to always load the file contents, deprecated the `Lcobucci\JWT\Signer\Key\LocalFileReference`, and suggest `Lcobucci\JWT\Signer\Key\InMemory` as the alternative. As a workaround, use `Lcobucci\JWT\Signer\Key\InMemory` instead of `Lcobucci\JWT\Signer\Key\LocalFileReference` to create the instances of one's keys.

Affected products

lcobucci jwt: from 3.4.0 before 3.4.6; from 4.0.0 before 4.0.4; from 4.1.0 before 4.1.5 — fixed in 3.4.6, 4.0.4, 4.1.5

How to fix

Upgrade to a fixed version: lcobucci jwt 3.4.6, 4.0.4, 4.1.5. Check the vendor advisory for mitigations.

References

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