CVE-2026-77205

A flaw was found in Libreswan's handling of malformed X.509 certificates when running in FIPS mode. A remote attacker may cause a rejected certificate to remain in the NSS certificate cache, resulting in legitimate certificates with the same serial number being rejected. This can prevent affected peers from establishing connections until the Libreswan service is restarted.

This vulnerability is rated as having a Low impact because exploitation requires the system to operate in FIPS mode and depends on an adversary correctly guessing or intercepting certificate serial numbers, making attack complexity as high. Furthermore, the issue only produces a targeted denial of service by temporarily preventing legitimate peers with matching serial numbers from connecting, without causing daemon crashes or compromising system data, indicating low impact to Availability.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Disabling FIPS mode will prevent this attack vector. However, disabling FIPS mode may violate security or compliance requirements and should not be used as a workaround without authorization.