CVE-2026-20956
Published: 13 January 2026
Summary
CVE-2026-20956 is a high-severity Untrusted Pointer Dereference (CWE-822) vulnerability in Microsoft Office Long Term Servicing Channel. Its CVSS base score is 7.8 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Client Execution (T1203); ranked at the 21.8th 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).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Flaw remediation requires applying Microsoft patches for the untrusted pointer dereference in Excel, directly eliminating the vulnerability and preventing local code execution.
Memory protection safeguards such as DEP, ASLR, and stack canaries mitigate untrusted pointer dereference exploits by preventing unauthorized code execution in Excel processes.
Malicious code protection scans and blocks malicious Excel documents exploiting the untrusted pointer dereference before they can trigger code execution.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Vulnerability enables local arbitrary code execution via malicious Excel document (user interaction), directly mapping to client-side exploitation and malicious file execution.
NVD Description
Untrusted pointer dereference in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
Deeper analysisAI
CVE-2026-20956, published on 2026-01-13, is an untrusted pointer dereference vulnerability (CWE-822) affecting Microsoft Office Excel. The issue enables an unauthorized attacker to execute code locally and carries a CVSS v3.1 base score of 7.8 (AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H), indicating high severity due to its potential for significant impacts on confidentiality, integrity, and availability.
Exploitation requires local access to the target system (AV:L) with low complexity (AC:L) and no privileges (PR:N), but relies on user interaction (UI:R), such as opening a malicious Excel document. A successful attack allows arbitrary code execution in the context of the user without scope change (S:U), potentially compromising the local system with high confidentiality, integrity, and availability impacts.
Mitigation details are available in the Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20956.
Details
- CWE(s)