CVE-2026-77205 Denial of Service via sending bogus X.509 certificates
Attackers can lock out legitimate peers by sending bogus certificates that persist in the cache, causing denial of service in FIPS mode.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-77205?
CVE-2026-77205 is a low-severity denial of service vulnerability in The Libreswan Project libreswan, published on 13 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Libreswan in FIPS mode has a vulnerability where badly formed received certificates are rejected, but not deleted from the NSS cache. As a result, any real certificates with the same serial number are rejected as well. This can be abused to lock out legitimate peers from connecting. The add_decoded_cert() function missed a call to CERT_DestroyCertificate() due to an incorrect fix for CVE-2026-14957. Sending bogus certificates with new serial numbers could prevent the real certificates with those serial numbers from connecting until the service has restarted.
Weakness: CWE-772
Which versions are affected by CVE-2026-77205?
How do I fix CVE-2026-77205?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-77205 being exploited?
There is no known exploitation of CVE-2026-77205 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-77205, GHSA-7m29-c28j-rg7h, UBUNTU-CVE-2026-77205.