Bug 2550631

Summary: CVE-2026-77205 libreswan: Denial of Service via sending bogus X.509 certificates [fedora-all]
Product: [Fedora] Fedora Reporter: TEJ RATHI <trathi>
Component: libreswanAssignee: Paul Wouters <paul.wouters>
Status: NEW --- QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: low Docs Contact:
Priority: low    
Version: rawhideCC: dueno, paul.wouters, shebburn
Target Milestone: ---Keywords: Security, SecurityTracking
Target Release: ---Flags: fedora-admin-xmlrpc: mirror+
Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["7ee9a452-b0ae-42de-908b-74510ab72f24"]}
Fixed In Version: Doc Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On:    
Bug Blocks: 2550255    

Description TEJ RATHI 2026-10-13 15:41:21 UTC 
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

The Libreswan Project received a report about an issue in the libreswan 5.3 series related to badly formed received certificates while running in FIPS mode. While being rejected, the certifiates were not deleted from the NSS cache, resulting in any real certificates with the same serial number being rejected as well. This can be abused to lock out legitimate peers from connecting.

Sending bogus certificates with new serial numbers could prevent the real certificates with those serial numbers from connecting until the service has restarted. While there is no RFC that dictates Certificate Authority (CA) should use randomized serial numbers, it is considered best practise and it is a requirement of the CA/Browser Forum. If using a private Root CA for IPsec VPNs, it is recommended to verify it uses randomized serial numbers.  However, an attacker could still trick a peer into connecting to them first, thus learning the serial number.

Vulnerable versions : 5.3, 5.3.1, 5.3.2
Not vulnerable      : 3.0 - 5.2, 5.4 and higher