Raw vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:HSummary
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 43th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
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.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-7351
Vulnerability Data
Improper input validation in Windows Hyper-V allows an authorized attacker to execute code locally.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 6 hardening rules · 3 OS baselines
V1.4.1
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation can discover missing input validation through analysis or test cases.
SI-10 directly requires validity checks on information inputs, structurally preventing improper or missing validation.
Requiring documented development standards and tools can embed input-validation practices into the engineering process.
Security engineering principles require use of memory-safe constructs and bounds-checked allocation routines that avoid introducing heap overflows.
Process isolation confines the effects of an out-of-bounds read to the compromised process.
Memory-protection mechanisms limit the ability of a heap overflow to execute attacker-controlled code or corrupt adjacent structures.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure-development practices directly require bounds checking and safe memory handling that prevent heap overflows.
Vulnerability scanning and recording can discover heap-overflow flaws but does not prevent their introduction in code.
Timely patching removes known heap-overflow instances after they exist.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Testing against a defined set of requirements and using code review plus vulnerability scanning forces validation of inputs and handling of unanticipated conditions, reducing the chance that malformed data will be accepted.
Logging can record evidence of an out-of-bounds read but does not prevent the weakness itself.
Secure-coding guidelines and mandatory security testing (including code scans) compel developers to validate and sanitize inputs at design and implementation time, lowering the incidence of malformed or malicious data reaching downstream components.
Mandating input controls that include integrity checks and input validation ensures that untrusted data is examined before use, blocking the root cause of many injection and malformed-data weaknesses.
Security-by-design principles explicitly call for data validation and sanitization at every layer, reducing the chance that malformed or malicious input will be processed without scrutiny.
Requiring language-specific secure coding standards, peer review, SAST and documented mitigation of common programming errors forces validation of all inputs before they are trusted.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
RHEL 8 (1 rule)
- V-230265 RHEL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-20