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CVE-2026-33824 – Double-Free Remote Code Execution in the Windows IKE/IPsec Extension

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Summary

CVE-2026-33824 is a critical double-free (CWE-415) remote code execution vulnerability in the Windows IKE (Internet Key Exchange) Extension (ikeext.dll), the service behind Windows IPsec / IKEv2 VPN. An unauthenticated, remote attacker can execute arbitrary code by sending specially crafted IKE traffic to UDP port 500 (IKE) or 4500 (NAT-T IKE) on a vulnerable Windows host. It carries a CVSS v3.1 score of 9.8 (Critical), is considered wormable, and was added to CISA’s Known Exploited Vulnerabilities (KEV) catalog on 2026-08-18 following observed in-the-wild exploitation.

Technical details

  • Root cause: a double-free (CWE-415) in the Windows IKE Extension (ikeext.dll) during reassembly of fragmented IKEv2 IKE_AUTH messages; improper ownership of a heap pointer causes the same allocation to be freed twice.
  • Trigger conditions: an attacker sends crafted IKE / IKEv2 packets to UDP 500 or 4500; no authentication or user interaction is required.
  • Attack vector: Network (AV:N), low complexity (AC:L), pre-authentication (PR:N), resulting in remote code execution in the context of the IKEEXT service.
  • Impact: full remote code execution. Because it is unauthenticated and network-reachable, the flaw is considered wormable.

Affected software

Unpatched Windows systems that run the IKE/IPsec service (IKEEXT), including:

  • Windows Server 2016, 2019, 2022, 2022 23H2, and 2025
  • Windows 10 (1607 through 22H2) and Windows 11 (23H2 through 26H1)

Systems that have not applied the April 2026 Microsoft security updates should be considered vulnerable.

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • CISA KEV: added 2026-08-18 (actively exploited)

Mitigation and recommended actions

  • Immediate: apply the Microsoft April 2026 security updates (or later) to all affected Windows hosts.
  • If immediate patching is not possible: restrict inbound access to UDP 500 / 4500 to trusted peers only, or disable the IKEEXT service on hosts that do not require IPsec / IKEv2 VPN.
  • Reduce exposure: ensure IKE/IPsec VPN endpoints are not needlessly exposed to the public internet.

References

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