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Vulnerability record · CVE-2026-41091 · published 20 May 2026

CVE-2026-41091: Microsoft Defender link following allows local privilege elevation

Microsoft · Malware Protection Engine

Microsoft Defender's malware protection engine resolves links improperly before accessing files, a link-following flaw (CWE-59). A local attacker with existing low-privilege access can abuse this to escalate to higher privileges on the host. It matters because Defender runs with high privilege on Windows endpoints, and CISA added it to KEV on the publication date.

7.8 CVSS 3.1 High CISA KEV since 20 May 2026 EPSS 0.44% · top 63.9% CWE-59 · Link following
7.8CVSS 3.1 base score
0.44%EPSS exploitation probability, 30 days
YesIn CISA KEV, fix deadline passed
1Affected product versions listed by NVD
2References
24 Jul 2026Last modified by NVD

Description

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

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 17 September 2026. Confidence: medium.

high priorityCVSS 7.8 with local privilege escalation and confirmed KEV listing, but exploitation requires existing local access and no ransomware use is documented.

What it is

Microsoft Defender's malware protection engine resolves links improperly before accessing files, a link-following flaw (CWE-59). A local attacker with existing low-privilege access can abuse this to escalate to higher privileges on the host. It matters because Defender runs with high privilege on Windows endpoints, and CISA added it to KEV on the publication date.

Impact

An authorized local attacker gains elevated privileges on the affected system, with high impact to confidentiality, integrity and availability per the CVSS vector. This can serve as a stepping stone to broader control of the endpoint.

Attack surface

Reached locally (AV:L) with low attack complexity and low privileges required (PR:L), and no user interaction (UI:N). No network vector or remote unauthenticated path is described.

Exploitation

CISA added this to the Known Exploited Vulnerabilities catalog on 2026-05-20 with a 2026-06-03 remediation due date, indicating known exploitation. EPSS 30-day probability is 0.08202 (94.6th percentile), and no ransomware campaign use is documented.

What to do

  • Apply the Microsoft update per the MSRC advisory for CVE-2026-41091 as the first action.
  • Follow CISA BOD 22-01 guidance for cloud services, or discontinue use if mitigations are unavailable, per the KEV required action.
  • Restrict and monitor local interactive and low-privilege accounts on endpoints running the affected Defender engine.
  • Verify Defender engine and platform versions are current after patching, since the record does not list affected versions.

Detection

  • Monitor for unexpected privilege changes or high-integrity process creation originating from low-privilege local users on Defender-managed hosts.
  • Audit file and link creation in paths the Defender engine accesses, looking for symlink or junction abuse preceding file access.
  • Alert on suspicious local process chains that touch Defender engine files or directories outside normal update activity.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.

Exploitation in the wild

CISA added CVE-2026-41091 to the Known Exploited Vulnerabilities catalog on 20 May 2026 as "Microsoft Defender Link Following Vulnerability". Required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Federal deadline 3 June 2026.

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-41091 Vendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-41091 Third Party AdvisoryUS Government Resource

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

7.8CVE-2017-8540Microsoft Malware Protection Engine out-of-bounds write via crafted fileThe Microsoft Malware Protection Engine, used by Windows Defender, Forefront, Security Essentials, System Center Endpoint Protection, Intune Endpoint…KEVEPSS 72%analysed9.3CVE-2013-1346Microsoft malware protection engine memory buffer overflow vulnerabilitympengine.dll in Microsoft Malware Protection Engine before 1.1.9506.0 on x64 platforms allows remote attackers to execute arbitrary code or cause a d…EPSS 12%9.3CVE-2006-5270Microsoft antigen vulnerabilityInteger overflow in the Microsoft Malware Protection Engine (mpengine.dll), as used by Windows Live OneCare, Antigen, Defender, and Forefront Securit…EPSS 30%8.1CVE-2026-45584Microsoft malware protection engine heap-based buffer overflow vulnerabilityHeap-based buffer overflow in Microsoft Defender allows an unauthorized attacker to execute code over a network.EPSS 0.71%7.8CVE-2026-69414Microsoft malware protection engine improper access control vulnerabilityMicrosoft is aware of an elevation of privilege in the Microsoft Malware Protection Engine in Microsoft Defender publicly referred to as "Shield…EPSS 0.33%7.8CVE-2026-55012Microsoft malware protection engine heap-based buffer overflow vulnerabilityInteger overflow or wraparound in Microsoft Defender allows an unauthorized attacker to execute code locally.EPSS 0.47%7.8CVE-2026-55011Microsoft malware protection engine vulnerabilityInteger underflow (wrap or wraparound) in Microsoft Defender allows an unauthorized attacker to execute code locally.EPSS 0.47%7.8CVE-2021-42298Microsoft malware protection engine code injection vulnerabilityMicrosoft Defender Remote Code Execution VulnerabilityEPSS 5.8%

Source: NIST National Vulnerability Database (record CVE-2026-41091), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.