CVE-2026-20871
Published: 13 January 2026
Summary
CVE-2026-20871 is a high-severity Use After Free (CWE-416) vulnerability in Microsoft Windows 10 21H2. Its CVSS base score is 7.8 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 8.2th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-16 (Memory Protection) and SI-2 (Flaw Remediation).
Deeper analysis
CVE-2026-20871 is a use-after-free vulnerability (CWE-416) in the Desktop Windows Manager (DWM), a core component of Microsoft Windows responsible for compositing windows and handling graphical effects. Published on January 13, 2026, it has a CVSS v3.1 base score of 7.8 (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H), indicating high impact potential from local exploitation.
An authorized local attacker with low privileges can exploit this vulnerability to achieve privilege escalation. By triggering the use-after-free condition in DWM, the attacker can execute arbitrary code with elevated privileges, potentially gaining SYSTEM-level access on the affected system without requiring user interaction.
The Microsoft Security Response Center (MSRC) has published an update guide at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20871, which provides details on available patches and mitigation recommendations for addressing this local privilege escalation vulnerability.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2171
Vulnerability details
Use after free in Desktop Windows Manager allows an authorized attacker to elevate privileges locally.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Direct local privilege escalation via exploitation of use-after-free in core Windows component (DWM) to achieve SYSTEM-level arbitrary code execution.
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Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly remediates the use-after-free flaw in DWM through timely patching as guided by MSRC updates.
Implements memory protection mechanisms such as ASLR, DEP, and guard pages to prevent exploitation of the use-after-free vulnerability in DWM.
Enforces least privilege on processes and accounts to limit the scope and success of local privilege escalation from low-privileged attackers.