CVE-2021-41106 is a low-severity (CVSS 3.3) CWE-345 vulnerability in lcobucci/jwt. A fix is available for lcobucci/jwt — see the affected versions and patch details below.
File reference keys leads to incorrect hashes on HMAC algorithms
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-41106 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
lcobucci/jwt🐘lcobucci/jwt🐘lcobucci/jwtReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | lcobucci/jwt | ≥ 3.4.0&&< 3.4.6 | 3.4.6composer require lcobucci/jwt:^3.4.6 |
| 🐘Packagist | lcobucci/jwt | ≥ 4.0.0&&< 4.0.4 | 4.0.4composer require lcobucci/jwt:^4.0.4 |
| 🐘Packagist | lcobucci/jwt | ≥ 4.1.0&&< 4.1.5 | 4.1.5composer require lcobucci/jwt:^4.1.5 |
Affected Products
jwtlcobucciDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for lcobucci/jwt, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update lcobucci/jwt to 3.4.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-41106 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2021-41106 in your dependencies?
Find it across Packagist, including transitive dependencies.