CVE-2026-33996: LibJWT has NULL/bounds validation in JWK octet and RSA PSS parsing

Severity: medium (CVSS 5.5 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: 2026-03-27 · updated 2026-06-17
Weakness: CWE-476

Description

LibJWT is a C JSON Web Token Library. Starting in version 3.0.0 and prior to version 3.3.0, the JWK parsing for RSA-PSS did not protect against a NULL value when expecting to parse JSON string values. A specially crafted JWK file could exploit this behavior by using integers in places where the code expected a string. This was fixed in v3.3.0. A workaround is available. Users importing keys through a JWK file should not do so from untrusted sources. Use the `jwk2key` tool to check for validity of a JWK file. Likewise, if possible, do not use JWK files with RSA-PSS keys.

Affected products

benmcollins libjwt: from 3.0.0 before 3.3.0 — fixed in 3.3.0

How to fix

Upgrade to a fixed version: benmcollins libjwt 3.3.0. Check the vendor advisory for mitigations.

References

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