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 IKEv2IKE_AUTHmessages; 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.
How IONIX identifies potentially affected assets
IONIX surfaces potentially affected assets by combining two signals already collected during discovery scanning, with no additional request sent to the asset:
- Network exposure: the asset responds on UDP port 500 (IKE/IPsec).
- Technology fingerprint: a Windows/Microsoft platform indicator derived from the asset’s HTTP/TLS response (for example Microsoft Windows, Windows Server, IIS, Microsoft HTTPAPI, Microsoft ASP.NET, Microsoft Exchange Server, Microsoft Terminal Services, or Microsoft SQL Server).
An asset that matches both signals is an internet-facing Windows host exposing IKE/IPsec, which is the profile targeted by CVE-2026-33824.
Accuracy disclaimer: this is an exposure signal, not a confirmation of vulnerability. IONIX cannot determine a host’s patch level remotely, so matched assets are candidates to verify rather than confirmed-vulnerable systems. The list may contain false positives (for example a Windows web server co-located with a non-Windows VPN appliance on the same address) and false negatives: Windows attribution relies on an HTTP/TLS fingerprint, so IKE/IPsec endpoints that expose no web service (many bare-IP VPN responders) cannot be attributed to an operating system externally and are not listed. Always confirm patch status directly on the affected host.