CVE-2026-29000 pac4j CVE debrief

Who should care

Users of pac4j-jwt versions prior to 4.5.9, 5.7.9, and 6.3.3 should be aware of this authentication bypass vulnerability and take steps to remediate. This includes operators, administrators, and security teams responsible for maintaining and securing systems that utilize pac4j-jwt for authentication.

Technical summary

The CVE-2026-29000 vulnerability is caused by a flaw in JwtAuthenticator when processing encrypted JWTs. This allows an attacker with the server's RSA public key to create a JWE-wrapped PlainJWT with arbitrary claims, effectively bypassing signature verification. As a result, an attacker can authenticate as any user, including administrators, without proper authentication. The vulnerability affects pac4j-jwt versions prior to 4.5.9, 5.7.9, and 6.3.3, and has a high impact on system security and integrity.

Defensive priority

High

Recommended defensive actions

• Upgrade pac4j-jwt to version 4.5.9, 5.7.9, or 6.3.3 or later
• Restrict access to the server's RSA public key
• Implement additional authentication mechanisms
• Monitor for suspicious authentication activity
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE-2026-29000 vulnerability was reported by Codeant. The NVD entry for CVE-2026-29000 provides additional details on the vulnerability. Evidence is limited to public sources and may not reflect the full scope or impact of the vulnerability. Defenders should verify affected systems and review official advisories for specific guidance.

Official resources