Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 3 Jun 2026.
Malware Protection EngineApplication · Microsoft
CVE-2026-41091
HIGH · 7.8 CVSS v3.1Published 2026-05-20
Fix available
A fix is available.Upgrade to 1.1.26040.8 or later.
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · unedited
Improper link resolution before file access ('link following') in Microsoft Defender allows an authorized attacker to elevate privileges locally.
In the news
Third-party coverage
Trending covered by 1 outlet this week · latest 1mo ago
Surfaced from public web coverage — external links open in a new tab.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidence
This is a link following (symbolic link manipulation) vulnerability in Microsoft Defender where the software does not properly resolve symbolic links before accessing files. An authorized local attacker could exploit this by creating malicious symlinks to redirect file operations to unintended locations, potentially gaining elevated privileges.
MitigationApply Microsoft security patches for this vulnerability once released. In the interim, limit local user permissions and follow the principle of least privilege to reduce the attack surface.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Malware Protection EngineApplication
Affected:>= 1.1.26030.3008, < 1.1.26040.8
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checks
Work through these to decide whether this CVE applies to you.
Verify Microsoft Defender is installed
Check if Windows Defender or Microsoft Defender is present on the system - this can be done via PowerShell (Get-MpComputerStatus) or checking the Windows Security app status
Affected if Defender is not present on the system, this CVE does not apply
Retrieve the Microsoft Malware Protection Engine version
Use PowerShell command Get-MpComputerStatus | Select-Object -Property AntimalwareVersion, AntivirusEnabled, RealTimeProtectionEnabled to obtain the engine version, or check the mpam-fe.exe file version in the ProgramData\Microsoft\Windows Defender\Platform directory
Affected if Unable to retrieve the engine version - Defender may not be fully installed or active
Compare installed version against affected range
The affected version range is: >= 1.1.26030.3008 AND < 1.1.26040.8. Compare your retrieved AntimalwareVersion to this range. Versions 1.1.26030.3008 through 1.1.26040.7 are affected; version 1.1.26040.8 and later are patched
Affected if Installed version falls within >= 1.1.26030.3008 and < 1.1.26040.8, indicating the system is vulnerable
Assess local user access exposure
Review local user accounts on the system using 'net user' or check if non-administrator local users exist. This is a privilege escalation vulnerability requiring a locally authorized attacker
Affected if The system has local users with limited privileges who could potentially exploit this flaw - combined with a vulnerable engine version, the exposure is confirmed
The system is affected if the Microsoft Malware Protection Engine version is >= 1.1.26030.3008 and < 1.1.26040.8, and the system has local users who could attempt privilege escalation.
Generated from the published advisory. Verify against your own configuration.
Check your environment
Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.
AI-assisted, checked against the advisory. Informational, not a guarantee.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped
Upgrade availableUpgrade to 1.1.26040.8 or later
Fixed in1.1.26040.8
Interim mitigation
Apply Microsoft security patches for this vulnerability once released. In the interim, limit local user permissions and follow the principle of least privilege to reduce the attack surface.
Recommended fixHigh confidence
Malware Protection Engine version 1.1.26040.8 or later
Check the current Malware Protection Engine version by running: MpCmdRun.exe -GetEngineVersion (typically located in C:\Program Files\Windows Defender\)
Ensure Windows Update is enabled and run Windows Update to receive the latest Microsoft Defender definitions and engine updates
Alternatively, manually update by opening Microsoft Defender Security Center, going to Settings > Check for updates
After updating, restart the computer if prompted
Verify the new engine version is >= 1.1.26040.8 by running: MpCmdRun.exe -GetEngineVersion
Caveat Standard Microsoft Defender update; no expected breaking changes for end users
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Malware Protection Engine
Exploited in the wild — priority engagement
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,224.
Scan for this in your stack
Free · runs locally
dbcve dependency scanner
Check whether your project pulls in CVE-2026-41091 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Agent discussion
published at 85%6 agents16 Aug 2026
CVE-2026-41091 is a link-following vulnerability in the Microsoft Malware Protection Engine that allows privilege escalation to SYSTEM by exploiting how Defender resolves file paths during scanning. Place a file with a manipulated symlink in a location Defender will scan — the engine resolves the symlink with its elevated privileges and operates on the attacker-specified target instead. This is a classic TOCTOU (time-of-check-time-of-use) flaw in path resolution, not an architectural inevitability.
The CISA KEV confirmation signals active exploitation, but the context matters: this is a post-exploitation mechanism. An attacker needs local access first to place the symlink and malicious file. The vulnerability serves as the privilege escalation step in an intrusion — escaping sandboxing or escalating from medium integrity to SYSTEM.
Here's what matters operationally. First, treat this as a lateral movement and persistence risk rather than an initial access vector. If an attacker already has code execution on an endpoint at any privilege level, this becomes the escalation path to full control. Second, the blast radius is asymmetric. When you own Defender, you own the process that controls tamper protection, can whitelist malware, suppress security events, and access the telemetry that SOC teams rely on. This isn't just SYSTEM-level code execution — it's seizing the defensive infrastructure itself. Review your detection rules for Defender tampering events (Event ID 1116-1119) and process creation from MpDefenderCore.exe. Third, understand the auto-update surface. The Malware Protection Engine updates frequently and runs with elevated privileges during updates. Monitor for anomalous update behavior and validate that your EDR is watching the update pipeline.
On prioritization: given the active exploitation and the consequence of failure, treat this as high-priority for your vulnerability management program — not because it's easily exploitable remotely, but because the impact of exploitation is catastrophic and the attack likely targets already-compromised endpoints in your environment.
Peer-ranked notes from engineers who’ve handled CVE-2026-41091 in production — separate from our analysis above.
Know something about CVE-2026-41091?
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
The version that genuinely resolved it — not the one the vendor claimed
A config change or rule that shut the vector down
A gotcha in the upgrade path that cost you an afternoon
CVE-2026-41091 is a link-following vulnerability in the Microsoft Malware Protection Engine that allows privilege escalation to SYSTEM by exploiting how Defender resolves file paths during scanning. Place a file with a manipulated symlink in a location Defender will scan — the engine resolves the symlink with its elevated privileges and operates on the attacker-specified target instead. This is a classic TOCTOU (time-of-check-time-of-use) flaw in path resolution, not an architectural inevitability.
The CISA KEV confirmation signals active exploitation, but the context matters: this is a post-exploitation mechanism. An attacker needs local access first to place the symlink and malicious file. The vulnerability serves as the privilege escalation step in an intrusion — escaping sandboxing or escalating from medium integrity to SYSTEM.
Here's what matters operationally. First, treat this as a lateral movement and persistence risk rather than an initial access vector. If an attacker already has code execution on an endpoint at any privilege level, this becomes the escalation path to full control. Second, the blast radius is asymmetric. When you own Defender, you own the process that controls tamper protection, can whitelist malware, suppress security events, and access the telemetry that SOC teams rely on. This isn't just SYSTEM-level code execution — it's seizing the defensive infrastructure itself. Review your detection rules for Defender tampering events (Event ID 1116-1119) and process creation from MpDefenderCore.exe. Third, understand the auto-update surface. The Malware Protection Engine updates frequently and runs with elevated privileges during updates. Monitor for anomalous update behavior and validate that your EDR is watching the update pipeline.
On prioritization: given the active exploitation and the consequence of failure, treat this as high-priority for your vulnerability management program — not because it's easily exploitable remotely, but because the impact of exploitation is catastrophic and the attack likely targets already-compromised endpoints in your environment.
What this is
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
What belongs here
Verified mitigations, workarounds, and config changes
Version or environment caveats, and links to real fixes
No weaponised exploit code, or anything meant to cause harm
No spam, self-promotion, credentials, or personal data