CVE-2026-21244: CVE-2026-21244: Heap-based buffer overflow in Windows Hyper-V allows an authorized attacker to execute cod…

What it is

Heap-based buffer overflow in Windows Hyper-V allows an authorized attacker to execute code locally.

Exploitation evidence

First exploit evidence seen: 2026-04-30 (earliest date across the sources below).

Exploited in the wild

No source on this site lists in-the-wild exploitation yet (CISA KEV, VulnCheck KEV).

Public exploit code

Exploit-DB

• EDB-52537: Windows 11 25H2 - Heap Overflow (2026-04-30)

Sources: Exploit-DB (OffSec).

How to fix it

Fixed versions

• microsoft windows 10 1607: upgrade to 10.0.14393.8868 or later
• microsoft windows 10 1809: upgrade to 10.0.17763.8389 or later
• microsoft windows 10 21h2: upgrade to 10.0.19044.6937 or later
• microsoft windows 10 22h2: upgrade to 10.0.19045.6937 or later
• microsoft windows 11 23h2: upgrade to 10.0.22631.6649 or later
• microsoft windows 11 24h2: upgrade to 10.0.26100.7781 or later
• microsoft windows 11 25h2: upgrade to 10.0.26200.7781 or later
• microsoft windows server 2016: upgrade to 10.0.14393.8868 or later
• microsoft windows server 2019: upgrade to 10.0.17763.8389 or later
• microsoft windows server 2022: upgrade to 10.0.20348.4711 or later
• microsoft windows server 2022 23h2: upgrade to 10.0.25398.2149 or later
• microsoft windows server 2025: upgrade to 10.0.26100.32313 or later

Derived from the NVD CPE configuration (versionEndExcluding / versionEndIncluding). Always confirm with the vendor advisory.

Vendor advisories and patches

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21244 (Vendor Advisory)

MITRE ATT&CK mitigations for this chain

• M1050 Exploit Protection (for T1203) : Security applications that look for behavior used during exploitation such as Windows Defender Exploit Guard (WDEG) and the Enhanced Mitigation Experience Toolkit (EMET) can be used to mitigate some exploitation behavior. Control flow integrity checking is another way to potentially identify and stop a software exploi
• M1051 Update Software (for T1203) : Perform regular software updates to mitigate exploitation risk. Keeping software up-to-date with the latest security patches helps prevent adversaries from exploiting known vulnerabilities in client software, reducing the risk of successful attacks.
• M1048 Application Isolation and Sandboxing (for T1203) : Browser sandboxes can be used to mitigate some of the impact of exploitation, but sandbox escapes may still exist. Other types of virtualization and application microsegmentation may also mitigate the impact of client-side exploitation. Risks of additional exploits and weaknesses in those systems may still exist.

Detection Generic guidance

• Execution: Watch for the service process spawning shells or script interpreters (cmd.exe, powershell, sh, bash, python) via EDR process-tree rules.

Response checklist Generic guidance

1. Inventory: find every instance of the affected product and version (include internet-facing and forgotten ones).
2. Patch or mitigate per the vendor advisory; if you cannot patch, remove internet exposure or apply the vendor workaround.
3. Assume compromise if the system was exposed before patching: hunt for the indicators in the advisory and review logs back to the disclosure date.
4. Rotate credentials and secrets stored on or used by the affected system if compromise cannot be ruled out.