Impersonation of VPN peers and potential DoS in Libreswan, a widely used VPN solution.
CVE-2026-50721
IKEv1 SIG length check flaw allows impersonation and DoS in Libreswan
Is CVE-2026-50721 being exploited?
Not confirmed. CVE-2026-50721 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.39% probability of exploitation in the next 30 days.
How severe is CVE-2026-50721?
CVE-2026-50721 is rated High with a CVSS score of 8.1. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-50721?
Yes. A fix has been recorded for CVE-2026-50721. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-50721 affect?
CVE-2026-50721 affects Libreswan (IKEv1). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-50721?
Upgrade Libreswan to patched release when available; monitor VPN endpoints
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote impersonation via forged IKE SIG payload; DoS via short hash; no RCE.
Patch when possible
- affected<= 5.3
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.