CVE-2026-41091

Description

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

Overview

State: PUBLISHED
Assigner (CNA): microsoft
CVSS severity: HIGH
CVSS score: 7.8 / 10
CVSS vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
Effective score: 7.8 / 10 HIGH source: CNA overview
MSRC score: 7.8 / 10 HIGH MS rating: Important · Elevation of Privilege
CWE(s): CWE-59
Reserved: 2026-04-16
Published: 2026-05-19 07:00 UTC
Last updated: 2026-05-26 07:00 UTC
Source: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/41xxx/CVE-2026-41091.json
Linked Threat: CVE-2026-41091 — Microsoft Defender: Microsoft Defender Link Following Vulnerability

CISA Known Exploited Vulnerabilities CISA KEV

CISA has confirmed in-the-wild exploitation of this CVE. Federal agencies must remediate by the due date below; private orgs should treat it as priority-1.

Vulnerability name: Microsoft Defender Link Following Vulnerability
Vendor / project: Microsoft
Product: Defender
Date added to KEV: 2026-05-20
Remediation due: 2026-06-03
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.
Ransomware campaign use: Unknown
CISA notes: https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-41091 ; https://nvd.nist.gov/vuln/detail/CVE-2026-41091
CISA listing: www.cisa.gov/known-exploited-vulnerabilities-catalog

NVD triage scoring NVD CVE 2.0

Layer NVD adds on top of the CNA's CVE record — published / last-modified timestamps, exploitability / impact subscores, and the FIRST.org EPSS probability that this CVE will be exploited in the wild in the next 30 days.

NVD published: 2026-05-20 13:16:29 UTC
NVD last modified: 2026-05-20 19:06:36 UTC
NVD CVSS v3.1: 7.8 / 10 HIGH source: secure@microsoft.com
NVD CVSS vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Exploitability subscore: 1.8 / 10
Impact subscore: 5.9 / 10
EPSS score: 0.0522 (probability of exploitation in next 30 days)
EPSS percentile: 90.06% vs all CVEs — higher = more likely to be exploited, as of 2026-05-24

European Union Vulnerability Database ENISA EUVD

ENISA's official EU repository for curated vulnerability intelligence. Carries a separate identifier (EUVD-YYYY-NNNN) and frequently exposes an earlier-published description + CVSS than NVD does.

EUVD ID: EUVD-2026-31101
Assigner: microsoft
Published: May 20, 2026, 1:09:13 PM
Updated: May 26, 2026, 4:57:25 PM
EUVD base score (CVSS 3.1): 7.8 / 10
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
EUVD-reported EPSS: 8.0100
Vendors: Microsoft
Products: Microsoft Malware Protection Engine (-)

Microsoft Malware Protection Engine (1.1.0.0 <1.1.26040.8)
Aliases: GHSA-h776-j9jw-992p

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

EUVD references (1)

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-41091

Microsoft Security Response Center MSRC

Microsoft's vendor-authoritative record from the Security Update Guide — its own CVSS score, impact, severity rating, exploit assessment, and KB-article fixes. Refreshed 2026-08-12 01:09 UTC (source: CVRF).

MS severity: Important
Impact: Elevation of Privilege
MS CVSS base score: 7.8 / 10 (temporal 6.8)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
Exploit assessment: Publicly Disclosed:Yes;Exploited:Yes;Latest Software Release:Exploitation Detected
Release: 2026-May

Microsoft remediations / KB articles (2)

Release Notes — Vendor Fix / Security Update (fixed build 1.1.26040.8)
https://docs.microsoft.com/en-us/microsoft-365/security/defender-endpoint/manage-updates-baselines-microsoft-defender-antivirus?view=o365-worldwide — None Available / Release Notes

Microsoft FAQ (2)

What privileges could be gained by an attacker who successfully exploited this vulnerability?

An attacker who successfully exploited this vulnerability could gain SYSTEM privileges.

References	Identification
Last version of the Microsoft Malware Protection Engine affected by this vulnerability	1.1.26030.3008
First version of the Microsoft Malware Protection Engine with this vulnerability addressed	Version 1.1.26040.8

See Manage Updates Baselines Microsoft Defender Antivirus for more information.

Microsoft Defender is disabled in my environment, why are vulnerability scanners showing that I am vulnerable to this issue?

Vulnerability scanners are looking for specific binaries and version numbers on devices. Microsoft Defender files are still on disk even when disabled. Systems that have disabled Microsoft Defender are not in an exploitable state.

Why is no action required to install this update?

In response to a constantly changing threat landscape, Microsoft frequently updates malware definitions and the Microsoft Malware Protection Engine. In order to be effective in helping protect against new and prevalent threats, antimalware software must be kept up to date with these updates in a timely manner.

For enterprise deployments as well as end users, the default configuration in Microsoft antimalware software helps ensure that malware definitions and the Microsoft Malware Protection Engine are kept up to date automatically. Product documentation also recommends that products are configured for automatic updating.

Best practices recommend that customers regularly verify whether software distribution, such as the automatic deployment of Microsoft Malware Protection Engine updates and malware definitions, is working as expected in their environment.

How often are the Microsoft Malware Protection Engine and malware definitions updated?

Microsoft typically releases an update for the Microsoft Malware Protection Engine once a month or as needed to protect against new threats. Microsoft also typically updates the malware definitions three times daily and can increase the frequency when needed.

Depending on which Microsoft antimalware software is used and how it is configured, the software may search for engine and definition updates every day when connected to the Internet, up to multiple times daily. Customers can also choose to manually check for updates at any time.

What is the Microsoft Malware Protection Engine?

The Microsoft Malware Protection Engine, mpengine.dll, provides the scanning, detection, and cleaning capabilities for Microsoft antivirus and antispyware software.

Windows Defender uses the Microsoft Malware Protection Engine. On which products is Defender installed and active by default?

Defender runs on all supported version of Windows.

Are there other products that use the Microsoft Malware Protection Engine?

Yes, Microsoft System Center Endpoint Protection, Microsoft System Center 2012 R2 Endpoint Protection, Microsoft System Center 2012 Endpoint Protection and Microsoft Security Essentials.

Does this update contain any additional security-related changes to functionality?

Yes. In addition to the changes that are listed for this vulnerability, this update includes defense-in-depth updates to help improve security-related features.

Affected products (1)

Vendor	Product	Versions	Platforms
Microsoft	Microsoft Malware Protection Engine	`-` (affected)	—

Affected products — CPE 2.3 (1) NVD

NVD's normalized CPE 2.3 matchers, used by vendor tools (vulnerability scanners, asset managers) for automated detection. Compare with the CNA's free-text "Affected products" section above.

cpe:2.3:a:microsoft:malware_protection_engine:*:*:*:*:*:*:*:*

Vendor references (1)

References embedded in the original CVE record by the assigning CNA.

Microsoft Defender Elevation of Privilege Vulnerability vendor-advisorypatch

Web references (18)

DuckDuckGo results ranked by threat-intel / vendor advisory domains. Generated by the 🔎 Find references (web) button above — same flow as the Remediations search.

None Available msrc
https://thehackernews.com/2026/05/microsoft-slams-public-zero-day.html tenable:thehackernews.com
https://www.infosecurity-magazine.com/news/microsoft-uncoordinated-zeroday/ tenable:www.infosecurity-magazine.com
https://www.bleepingcomputer.com/news/microsoft/critical-windows-netlogon-remote-code-execution-flaw-now-exploited-in-attacks/ tenable:www.bleepingcomputer.com
https://thehackernews.com/2026/05/microsoft-warns-of-two-actively.html tenable:thehackernews.com
https://www.bleepingcomputer.com/news/security/microsoft-warns-of-new-defender-zero-days-exploited-in-attacks/ tenable:www.bleepingcomputer.com
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-41091 tenable:www.cisa.gov
https://www.cisa.gov/news-events/alerts/2026/05/20/cisa-adds-seven-known-exploited-vulnerabilities-catalog tenable:www.cisa.gov
https://www.cve.org/CVERecord?id=CVE-2026-41091 tenable:www.cve.org
https://www.darkreading.com/cyberattacks-data-breaches/exploits-turn-windows-defender-attacker-tool tenable:www.darkreading.com
https://www.first.org/epss/ tenable:www.first.org
https://www.helpnetsecurity.com/2026/05/21/microsoft-defender-vulnerabilities-cve-2026-41091-cve-2026-45498/ tenable:www.helpnetsecurity.com
https://www.pcworld.com/article/3116311/unpatched-microsoft-defender-flaw-lets-hackers-gain-admin-access.html tenable:www.pcworld.com
https://deadeclipse666.blogspot.com/2026/04/public-disclosure-response-for-cve-2026.html tenable:deadeclipse666.blogspot.com
https://www.securityweek.com/microsoft-patches-exploited-undefend-and-redsun-defender-zero-days/ tenable:www.securityweek.com
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-41091 tenable:msrc.microsoft.com
https://nvd.nist.gov/vuln/detail/CVE-2026-41091 tenable:nvd.nist.gov
https://securityaffairs.com/192508/security/u-s-cisa-adds-microsoft-and-adobe-flaws-to-its-known-exploited-vulnerabilities-catalog.html tenable:securityaffairs.com

NVD-tagged references (2)

Reference list NVD curates from the CNA record, vendor advisories, and third-party reports. The tag chips below are NVD's analyst-assigned categories.

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-41091 secure@microsoft.com Vendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-41091 134c704f-9b21-4f2e-91b3-4a467353bcc0 US Government ResourceThird Party Advisory

Indicators (2)

IOCs linked to the auto-promoted Threat row.

Type	Value	VirusTotal	Attached
cwe	`CWE-59`	no local data	2026-05-21 13:47 UTC
cve	`CVE-2026-41091`	no local data	2026-05-20 22:08 UTC

Remediations (9)

Remediations are stored against the linked Threat row; the list below is deduplicated across both pages.

CVE-2026-41091 - High Vulnerability - TheHackerWire

web:www.thehackerwire.com

CVE-2026-41091 is a High severity vulnerability (CVSS 7.8). Improper link resolution before file access ('link following') in Microsoft Defender allows an authorized attacker to elevate privileges locally.

2026-05-20 22:08 UTC
Microsoft addresses 137 vulnerabilities in May's Patch Tuesday ...

web:cyberscoop.com

Threats Microsoft addresses 137 vulnerabilities in May's Patch Tuesday, including 13 rated critical The high volume of vulnerabilities reflects a growing trend researchers have been anticipating as artificial intelligence models are deployed to find previously uncovered defects in code.

2026-05-20 22:08 UTC
CISA warns of active exploit in Microsoft Defender CVE-2026-41091

web:cybersixt.com

A patch is available from Microsoft via the advisory linked in the KEV note. Because the entry appears in the KEV catalogue, active exploitation has been confirmed in the wild. No known ransomware campaign has been linked to this CVE at this time. CISA has set a remediation deadline of 26 June 2026 for federal agencies to address the issue.

2026-05-20 22:08 UTC
Nvd - Cve-2026-41091

web:nvd.nist.gov

An official website of the United States government NVD MENU

2026-05-20 22:08 UTC
Security Update Guide - Microsoft

web:portal.msrc.microsoft.com

The Security Update Guide provides information on the latest Microsoft security updates, helping users understand and address potential vulnerabilities effectively.

2026-05-20 22:08 UTC
Microsoft Patch Tuesday, April 2026 Security Update Review

web:threatprotect.qualys.com

With Qualys Policy Audit's out-of-the-box mitigation or Compensatory Controls, which reduce the risk of a vulnerability being exploited because the remediation ( fix / patch ) cannot be done immediately, these security controls are not recommended by any industry standards, such as CIS and DISA-STIG.

2026-05-20 22:08 UTC
CVE-2026-41091 - Vulnerability Details - OpenCVE

web:app.opencve.io

Remediation No vendor fix or workaround currently provided. OpenCVE Recommended Actions Install the latest security update for Microsoft Defender from the Microsoft Security Response Center (see https://msrc.microsoft.com/update-guide/vulnerability/ CVE - 2026 - 41091 ).

2026-05-20 22:08 UTC
CVE-2026-41091 | Tenable®

web:www.tenable.com

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

2026-05-20 22:08 UTC
CISA Required Action

CISA KEV (via KEVin)

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Due date: 2026-06-03

2026-05-20 22:08 UTC

AI Forensic Analysis

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Raw JSON

The full cvelistV5 record. Download as CVE-2026-41091.json.

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