UPDATE — CVE-2026-33824 (Windows IKE Extension) is now on CISA's exploited catalogue, four months after the patch, while Microsoft's own record still reads 'Exploitation Less Likely'

UPDATE · originally covered UPDATE — the root cause of CVE-2026-33824 is published: a pre-authentication double free on the IKEv2 fragment-reassembly path, reachable on UDP 500/4500 against any Windows IKEv2 responder (2026-08-10)

the double free in the Windows IKE and AuthIP IPsec Keying Modules service is now catalogued as exploited. CISA added CVE-2026-33824 to its Known Exploited Vulnerabilities catalog on 2026-08-18, recording it as a double free that "could enable remote code execution" (CISA KEV catalog, 2026-08-18), ENISA's EU Vulnerability Database carries the same 2026-08-18 date and an EPSS of 55.85 for its corresponding record, though as a mirror of CISA's determination rather than a second assessment of it (ENISA EUVD, 2026-08-18). The prior entry recorded this flaw as patched with exploitation reported as no; that is the part that changed, and it is the only part.

The mechanism and the remediation are unchanged from the earlier coverage: the flaw sits on the IKEv2 fragment-reassembly path, needs no authentication and no user interaction, and yields code execution in the Local System context that hosts the IKEEXT service. What the exploitation confirmation changes is which hosts are in scope, because the vulnerable surface is not only the VPN concentrator — Microsoft's affected list spans Windows Server 2016 through 2025 and Windows 10 v1607 through Windows 11 v26H1, so any domain member that answers IKE, including a Routing and Remote Access role nobody remembers enabling, is a responder (ENISA EUVD, 2026-08-18).

The sourcing split is itself the operationally useful part. Microsoft's record has not been revised since it was published on 14 April 2026, and it still records exploitation as no with an exploitability assessment of "Exploitation Less Likely" (Microsoft Security Response Center, 2026-04-14). Any triage pipeline that ranks Windows CVEs on the vendor's own exploitability field — a common and otherwise reasonable design — has this flaw sitting four months deep in a patch backlog while two cataloguing authorities now class it as exploited. Neither authority publishes the telemetry behind its determination, and neither names an actor, so nothing here supports an attribution.

Detection and hunting concentrate on the service rather than the packet, because the trigger is a malformed fragment sequence that no ordinary log records as anomalous. In process and service telemetry, the signals are unexpected termination, restart or crash-dump generation for the host process running the IKE and AuthIP IPsec Keying Modules service, and any child process created under it — that service should never spawn a command interpreter or a script host. In network telemetry, inbound UDP 500 and 4500 flows from source addresses outside the known VPN peer set are the exposure indicator, and fragmented IKE traffic volumes that do not match the peer population are worth a look. Triage: a legitimate IKEv2 negotiation produces the same port pair and the same fragmentation, so traffic shape alone does not discriminate — what separates suspicious from normal is the source address falling outside the configured peer set, and the correlation of that flow with a service fault or a new child process on the responder. Microsoft's own interim guidance is a firewall control rather than a configuration change: block inbound UDP 500 and 4500 where IKE is unused, and restrict them to known peers where it is required (Microsoft Security Response Center, 2026-04-14).