CVE-2026-41091: Microsoft Defender High-Severity Vulnerability

What is CVE-2026-41091?

Improper link resolution before file access ('link following') in Microsoft Defender allows an authorized attacker to elevate privileges locally.

Technical Analysis

Weakness Classification

This vulnerability is classified as CWE-59.

Attack Vector Breakdown

• Attack Vector: Local
• Attack Complexity: Low
• Privileges Required: Low
• User Interaction: None
• Scope: Unchanged
• Confidentiality: High
• Integrity: High
• Availability: High

Impact Analysis

Exploitation requires local access to the target system, such as a local user session or a malicious file opened by a user. The attack complexity is low, meaning exploitation does not depend on specialized conditions or race windows. Successful exploitation can result in full confidentiality breach (complete data disclosure), complete integrity compromise (data modification or code execution), total availability loss (denial of service).

Exploitation Probability (EPSS): 9.5% chance of exploitation in the next 30 days (93th percentile). While the base probability may appear low, inclusion in CISA KEV confirms real-world exploitation is already occurring.

Is CVE-2026-41091 being exploited?

Yes. CVE-2026-41091 is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, restricted to CVEs with confirmed active exploitation in the wild. CISA added this vulnerability on 2026-05-20. Inclusion in KEV triggers the patching mandate under BOD 22-01 for U.S. federal civilian agencies, with a remediation deadline of 2026-06-03.

How to fix CVE-2026-41091

Apply the latest security update via Windows Update, WSUS, or Microsoft Update Catalog. For enterprise environments, use SCCM/Intune for managed deployment. If the patch cannot be applied immediately, check the MSRC advisory for workarounds such as registry-based mitigations or disabling affected features. Check the Microsoft Security Response Center page for the specific patch or update. CISA's Known Exploited Vulnerabilities catalog requires U.S. federal agencies to remediate this vulnerability by the due date shown below under Binding Operational Directive 22-01. Private organizations should treat KEV entries as priority-one patches because active exploitation has been confirmed in the wild.

Related Vulnerabilities

Other actively exploited vulnerabilities affecting Defender or sharing the same weakness (CWE-59):

• CVE-2026-45498 (Medium 4.0) [same product] — Microsoft Defender Denial of Service Vulnerability
• CVE-2026-33825 (High 7.8) [same product] — Insufficient granularity of access control in Microsoft Defender allows an…
• CVE-2025-60710 (High 7.8) [same vendor + same CWE] — Improper link resolution before file access ('link following') in Host Process…
• CVE-2008-4250 (Critical 9.8) [same vendor] — The Server service in Microsoft Windows 2000 SP4, XP SP2 and SP3, Server 2003…
• CVE-2009-1537 (High 8.8) [same vendor] — Unspecified vulnerability in the QuickTime Movie Parser Filter in quartz.dll…

Frequently asked questions

Is CVE-2026-41091 critical?

CVE-2026-41091 has a CVSS 3.1 base score of 7.8 — High severity. It should be treated as a priority patch, especially given the active exploitation confirmed by CISA.

Is CVE-2026-41091 being actively exploited?

Yes — CISA added CVE-2026-41091 to the Known Exploited Vulnerabilities catalog on 2026-05-20. Inclusion in KEV means CISA has confirmed in-the-wild exploitation.

How do I patch CVE-2026-41091?

Apply the security update from Microsoft for Defender. Federal agencies must remediate by 2026-06-03 under BOD 22-01. Refer to the Microsoft Security Response Center for the official patch.

What type of vulnerability is CVE-2026-41091?

CVE-2026-41091 is classified under CWE-59.

What is the CVSS score for CVE-2026-41091?

CVE-2026-41091 has a CVSS 3.1 base score of 7.8, classifying it as High severity. The attack vector is Local, attack complexity is Low, and non-zero privileges are required.