CVE-2026-20820
Published: 13 January 2026
Summary
CVE-2026-20820 is a high-severity Heap-based Buffer Overflow (CWE-122) vulnerability in Microsoft Windows Server 2008. 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 8.5th 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-2 (Flaw Remediation) and AC-6 (Least Privilege).
Deeper analysis
CVE-2026-20820, published on 2026-01-13, is a heap-based buffer overflow vulnerability (CWE-122) in the Windows Common Log File System Driver. It carries a CVSS v3.1 base score of 7.8, with vector AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. The flaw affects Windows systems that utilize this driver for common log file system operations.
A local attacker with low privileges (PR:L) can exploit the vulnerability due to its low attack complexity (AC:L) and lack of required user interaction (UI:N). Successful exploitation enables privilege escalation, granting high-impact access to confidentiality, integrity, and availability (C:H/I:H/A:H) on the affected system.
Microsoft's update guide provides details on mitigation, available at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20820.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2211
Vulnerability details
Heap-based buffer overflow in Windows Common Log File System Driver allows an authorized attacker to elevate privileges locally.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Heap buffer overflow in CLFS driver directly enables local privilege escalation from low-privileged context (T1068).
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Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Timely application of Microsoft patches directly remediates the heap-based buffer overflow vulnerability in the Windows Common Log File System Driver, preventing local privilege escalation.
Memory protection mechanisms such as non-executable heap regions and address space randomization mitigate exploitation of the heap buffer overflow for code execution and privilege escalation.
Enforcing least privilege on local user accounts limits the attack surface and potential impact of privilege escalation via the driver vulnerability.