Critical Authentication Bypass Vulnerability Discovered in pac4j-jwt Java Library
In March 2026, a critical authentication bypass vulnerability (CVE-2026-29000) was discovered in the pac4j-jwt Java library, affecting versions prior to 4.5.9, 5.7.9, and 6.3.3. This flaw allows remote attackers to forge authentication tokens by exploiting improper verification of cryptographic signatures in the JwtAuthenticator component when processing encrypted JSON Web Tokens (JWTs). By crafting a JWE-wrapped PlainJWT with arbitrary subject and role claims, attackers can bypass signature verification and authenticate as any user, including administrators. ([arcticwolf.com](https://arcticwolf.com/resources/blog/cve-2026-29000/?utm_source=openai)) The vulnerability poses a significant risk due to the widespread use of pac4j-jwt in various Java applications and frameworks. Organizations utilizing affected versions are urged to upgrade to the latest fixed releases immediately to mitigate potential exploitation. ([arcticwolf.com](https://arcticwolf.com/resources/blog/cve-2026-29000/?utm_source=openai))
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