CVE-2026-20840
Published: 13 January 2026
Summary
CVE-2026-20840 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 8.6th 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-2026-20840 is a heap-based buffer overflow vulnerability in the Windows NTFS file system component. Published on 2026-01-13, it carries a CVSS v3.1 base score of 7.8 (High), with vector AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H, and is associated with CWE-122.
A local attacker with low privileges (PR:L) can exploit this vulnerability through local access with low attack complexity and no user interaction. Successful exploitation enables arbitrary code execution, resulting in high impacts to confidentiality, integrity, and availability.
Mitigation guidance is available in the Microsoft Security Update Guide at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20840.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2178
Vulnerability details
Heap-based buffer overflow in Windows NTFS allows an authorized attacker to execute code locally.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Local heap buffer overflow in NTFS driver directly enables arbitrary code execution from low-privileged context, mapping to Exploitation for Privilege Escalation.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly mandates timely patching and remediation of vulnerabilities like the heap-based buffer overflow in Windows NTFS to prevent exploitation.
Provides memory protection mechanisms such as DEP, ASLR, and stack guards that specifically mitigate heap buffer overflow exploits leading to code execution.
Enforces least privilege for local low-privilege accounts (PR:L), limiting the attack surface and potential impact of NTFS exploitation.