Authentication Bypass in JwtAuthenticator of pac4j-jwt by pac4j

CVE-2026-29000

What is CVE-2026-29000?

CVE-2026-29000 is a critical vulnerability identified in the JwtAuthenticator component of the pac4j-jwt library by Pac4j. This library is widely utilized for securing applications through JSON Web Token (JWT) authentication, which is a common method for transmitting information between parties in a secure and verifiable manner. The vulnerability allows remote attackers to bypass authentication processes by forging authentication tokens. When exploited, this flaw enables attackers who possess the server's RSA public key to create fraudulent JWE-wrapped tokens containing arbitrary claims, effectively allowing them to authenticate as any user, including administrators. This undermines the integrity and security of the authentication mechanism, posing significant risks to organizations that rely on this software for secure access control.

Potential impact of CVE-2026-29000

1. Unauthorized Access: The vulnerability permits attackers to impersonate any user within the system, including those with administrative privileges. This unauthorized access could lead to malicious activities such as data theft, modification of sensitive information, or manipulation of system settings.

2. Compromise of Sensitive Data: Given that attackers can authenticate as any user, they may gain access to confidential data stored within the application. This could lead to severe data leaks, impacting both organizational privacy and compliance with data protection regulations.

3. Exploitation in The Wild: There have been indications that this vulnerability could be actively exploited in cyber attacks. The potential for exploitation emphasizes the urgency of addressing the vulnerability, as it could facilitate further attacks, including the deployment of ransomware or other malicious payloads targeting involved systems.

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