CVE-2026-12413 Libreswan Vulnerability
An invalidly formatted IKEv2 fragment causes the Libreswan pluto daemon to crash and restart. Continued exploitation would cause a denial of service. The function reassemble_v2_incoming_fragments() would ignore unknown outer payloads but still store these in a fixed size array msg_digest.digest[PAYLIMIT]. An off-by-one error in the assertion PASSERT(logger, md->digest_roof < elemsof(md->digest)) causes the daemon to abort. No remote code execution is possible. Any configuration that allows IKEv2 connections that do not set fragmentation=no are vulnerable. IKEv1 is not affected.
Quick answer
Libreswan should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- Libreswan 4.6 through 5.3
Fixed versions
- Libreswan 5.3.1 or later
- Vendor backported patch for CVE-2026-12413
How to fix it
CVE-2026-12413 affects Libreswan. The affected range is Libreswan 4.6 through 5.3. Update to Libreswan 5.3.1 or later, Vendor backported patch for CVE-2026-12413. Fix exposed systems first, especially where internet-facing services, admin panels, and trusted internal users can be reached. If abuse is suspected, review logs and rotate secrets that may have been exposed.
- Inventory every Libreswan install and note the exact version.
- Compare each install with the affected range: Libreswan 4.6 through 5.3.
- Update to Libreswan 5.3.1 or later, Vendor backported patch for CVE-2026-12413.
- If you cannot patch today, restrict internet-facing services, admin panels, and trusted internal users to trusted users and networks.
- Back up the current configuration before changing production systems.
- Review recent logs for crashes, strange admin actions, failed logins, or unexpected access.
- Rotate passwords, tokens, certificates, or keys if compromise is suspected.
- Document the change, owner, date, and final version.
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Verify the fix
- Confirm the installed version now matches the fixed guidance: Libreswan 5.3.1 or later, Vendor backported patch for CVE-2026-12413.
- Confirm old affected versions are no longer deployed: Libreswan 4.6 through 5.3.
- Confirm internet-facing services, admin panels, and trusted internal users is limited to the smallest needed group.
- Rerun the relevant Fixnx scan or internal security check after the change.
- Save logs, screenshots, or package output as proof of the fix.
Related categories
Trusted references
FAQ
What is affected by CVE-2026-12413?
Libreswan versions listed as affected should be reviewed: Libreswan 4.6 through 5.3.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.