CVE-2026-21247
Published: 10 February 2026
Summary
CVE-2026-21247 is a high-severity Improper Input Validation (CWE-20) vulnerability in Microsoft Windows 11 23H2. Its CVSS base score is 7.3 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 19.2th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
Threat & Defense at a Glance
Threat & Defense Details
Likely Mitigating ControlsAI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Security testing and developer training directly verify and enforce proper input validation, reducing exploitability of injection and malformed-data weaknesses.
Security testing and evaluation at multiple SDLC stages directly detects missing or flawed input validation, with the required remediation process ensuring fixes are applied.
Directly implements checks on information inputs to reject invalid data before processing.
Spam protection mechanisms perform filtering and detection on inbound/outbound messages, directly compensating for missing or weak input validation of unsolicited content.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Local improper input validation in Hyper-V hypervisor directly enables exploitation for privilege escalation (T1068) from low-priv local user to arbitrary code execution on host; user interaction requirement also maps to exploitation for client execution (T1203).
NVD Description
Improper input validation in Windows Hyper-V allows an authorized attacker to execute code locally.
Deeper analysisAI
CVE-2026-21247 is an improper input validation vulnerability (mapped to CWE-20, CWE-122, and CWE-125) in the Windows Hyper-V hypervisor component of Microsoft Windows operating systems. It enables an authorized local attacker to execute arbitrary code on the host system. The vulnerability carries a CVSS v3.1 base score of 7.3 (AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H), indicating high impact potential with low attack complexity, local access vector, low privilege requirements, and user interaction needed.
An attacker with local access and low privileges, such as a standard user on the Hyper-V host, can exploit this flaw by providing malformed input that triggers improper validation during Hyper-V operations. Successful exploitation requires the user to interact, such as opening a malicious file or performing a specific action within the Hyper-V environment. This leads to arbitrary code execution in the context of the Hyper-V process, potentially compromising confidentiality, integrity, and availability with high severity on the affected host.
Mitigation details are available in the Microsoft Security Response Center (MSRC) update guide at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21247, which was published on 2026-02-10. Security practitioners should consult this advisory for patching instructions and workarounds.
Details
- CWE(s)