CVE-2026-29000: Authentication Bypass in pac4j-jwt Java Library
On March 03, 2026, pac4j released fixes for a maximum severity vulnerability in pac4j-jwt, tracked as CVE-2026-29000. The flaw arises from improper verification of cryptographic signatures in the JwtAuthenticator component when processing encrypted JWTs (JWE). A remote, unauthenticated threat actor who knows the server’s RSA public key can bypass authentication and impersonate arbitrary users (including administrators) by submitting a crafted JWE whose inner token is an unsigned PlainJWT.