Executive brief
A security flaw in the pac4j-jwt library, which handles user authentication for Java applications, allows attackers to bypass security checks. By exploiting this issue, an unauthorized person can create fake login credentials to gain full access to the system, including administrative privileges. This could lead to the theft of sensitive customer data or complete control over the affected application.
Technical details
An authentication bypass vulnerability exists in the JwtAuthenticator component of pac4j-jwt due to improper verification of cryptographic signatures (CWE-347) when processing encrypted JSON Web Tokens (JWTs). Specifically, the library fails to properly validate the signature of a PlainJWT when it is wrapped within a JSON Web Encryption (JWE) structure. A remote, unauthenticated attacker who possesses the server's RSA public key can craft a malicious JWE-wrapped token containing arbitrary subject and role claims. This allows the attacker to bypass signature verification entirely and authenticate as any user, including administrators. The issue is resolved in versions 4.5.9, 5.7.9, and 6.3.3.
Affected products
- pac4j pac4j-jwt >= 4.0, < 4.5.9; >= 5.0, < 5.7.9; >= 6.0, < 6.3.3
Timeline
- 2026-03-04: advisory: Initial disclosure by VulnCheck and NVD
- 2026-03-04: patched: Fixes released in versions 4.5.9, 5.7.9, and 6.3.3