What’s Vulnerable › Vulnerabilities

CVE-2026-29000: pac4j-jwt JwtAuthenticator Authentication Bypass

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 6.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-03-04 · updated 2026-10-08
• Weakness: CWE-347

Description

pac4j-jwt versions prior to 4.5.9, 5.7.9, and 6.3.3 contain an authentication bypass vulnerability in JwtAuthenticator when processing encrypted JWTs that allows remote attackers to forge authentication tokens. Attackers who possess the server's RSA public key can create a JWE-wrapped PlainJWT with arbitrary subject and role claims, bypassing signature verification to authenticate as any user including administrators.

Affected products

• pac4j-jwt: from 4.0 before 4.5.9; from 5.0 before 5.7.9; from 6.0 before 6.3.3 — fixed in 4.5.9, 5.7.9, 6.3.3

How to fix

Upgrade to a fixed version: pac4j-jwt 4.5.9, 5.7.9, 6.3.3. Check the vendor advisory for mitigations.

References

• https://www.codeant.ai/security-research/pac4j-jwt-authentication-bypass-public-key
• https://www.pac4j.org/blog/security-advisory-pac4j-jwt-jwtauthenticator.html
• https://www.vulncheck.com/advisories/pac4j-jwt-jwtauthenticator-authentication-bypass

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