CVE-2026-77206 The Libreswan Project CVE debrief

Who should care

Defenders responsible for Libreswan deployments, particularly those using IKEv2 connections, should assess exposure and prioritize patching. This includes reviewing IKEv2 connection configurations to prevent exploitation and verifying patch application for affected Libreswan versions. Security teams and vulnerability management teams should also review the CVE record and source item for details on the null pointer dereference bug in Libreswan's IKEv2 state

Why it matters

A null pointer dereference bug in Libreswan's IKEv2 state machine EAP handling code can cause a crash and restart of the pluto daemon, potentially leading to a denial of service. Defenders should prioritize verifying and applying patches for affected Libreswan versions and review IKEv2 connection configurations.

• Potential denial of service due to repeated crashes and restarts of the pluto daemon.
• Verification of patch application for affected Libreswan versions.
• Review of IKEv2 connection configurations to prevent exploitation.
• Monitoring for potential attacks targeting this vulnerability.

Technical summary

The Libreswan project's IKEv2 state machine has a null pointer dereference bug in the EAP handling code for authentication. This bug can be triggered by any IKEv2 connection, even if EAP is not configured, and results in a crash and restart of the pluto daemon. The error is caused by a fall-through where it incorrectly dereferences ike->sa.st_eap which is NULL. A malicious IKE_AUTH packet can trigger this bug, meaning the peer does not need to be authenticated. No remote code execution is possible. Continued exploitation can cause a denial of service.

Defensive priority

Defenders should prioritize verifying and applying patches for Libreswan versions 4.7 to 5.3.2 and 5.4.

Recommended defensive actions

• Verify and apply patches for Libreswan versions 4.7 to 5.3.2 and 5.4.
• Monitor for potential denial of service attacks.
• Review and update IKEv2 connection configurations.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.

Evidence notes

The CVE record and source item provide details on the null pointer dereference bug in Libreswan's IKEv2 state machine EAP handling code. The bug can be triggered by any IKEv2 connection, even if EAP is not configured. The error is caused by a fall-through where it incorrectly dereferences ike->sa.st_eap which is NULL. A malicious IKE_AUTH packet can trigger this bug, meaning the peer does not need to be authenticated. Continued exploitation can cause a denial of service. The Libreswan project has provided patches for affected versions

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.