CVE-2026-40458

Description

PAC4J is vulnerable to Cross-Site Request Forgery (CSRF). A malicious attacker can craft a specially designed website which, when visited by a user, will automatically submit a forged cross-site request with a token whose hash collides with the victim's legitimate CSRF token. Importantly, the attacker does not need to know the victim’s CSRF token or its hash prior to the attack. Collisions in the deterministic String.hashCode() function can be computed directly, reducing the effective token's security space to 32 bits. This bypasses CSRF protection, allowing profile updates, password changes, account linking, and any other state-changing operations to be performed without the victim's consent. This issue was fixed in PAC4J versions 5.7.10 and 6.4.1.

How to fix CVE-2026-40458

To remediate CVE-2026-40458, upgrade the affected package to a fixed version below.

• —upgrade to 5.7.10 or later

Is CVE-2026-40458 being exploited?

Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.

Affected packages (1)

• from 0, < 5.7.10

CVSS scores

References (4)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-40458
• PATCHgithub.com/pac4j/pac4j
• WEBcert.pl/en/posts/2026/04/CVE-2026-40458
• WEBwww.pac4j.org/blog/security-advisory-pac4j-core-and-ldap.html