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Malware Protection EngineApplication · Microsoft

CVE-2026-45584

HIGH · 8.1 CVSS v3.1 Published 2026-05-20
Fix available
A fix is available. Upgrade to 1.1.26040.8 or later.
See remediation →
90/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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
Heap-based buffer overflow in Microsoft Defender allows an unauthorized attacker to execute code over a network.

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

A heap-based buffer overflow vulnerability exists in Microsoft Defender that allows an unauthorized remote attacker to execute arbitrary code. The vulnerability stems from improper bounds checking when processing network-based inputs, enabling memory corruption that can be leveraged for code execution with the privileges of the Defender process.

MitigationApply vendor-supplied patches for Microsoft Defender immediately; until then, minimize network exposure of systems running Defender and monitor for suspicious Defender process behavior.

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
Network
Complexity
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:H/PR:N/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.

  1. Check Microsoft Malware Protection Engine version
    Open PowerShell as Administrator and run: Get-MpComputerStatus | Select-Object AntivirusEngineVersion
    Affected if The displayed version is 1.1.26030.3008 or higher but lower than 1.1.26040.8
  2. Verify real-time protection is enabled
    In PowerShell, run: Get-MpComputerStatus | Select-Object RealTimeProtectionEnabled
    Affected if RealTimeProtectionEnabled returns True, meaning Defender actively scans files and network traffic
  3. Confirm Windows Defender Antivirus is the active antivirus
    Run: Get-MpComputerStatus | Select-Object AntivirusEnabled
    Affected if AntivirusEnabled returns True, indicating Windows Defender is the active security solution
  4. Review recent defender update status
    Run: Get-MpComputerStatus | Select-Object AntivirusSignatureLastUpdated
    Affected if The signatures have not been updated since the patch version 1.1.26040.8 was released, indicating the vulnerable engine version may still be in use

If the Microsoft Malware Protection Engine version falls between 1.1.26030.3008 (inclusive) and 1.1.26040.8 (exclusive), and real-time protection is active, the environment is vulnerable to CVE-2026-45584.

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 available Upgrade to 1.1.26040.8 or later
Fixed in 1.1.26040.8
Interim mitigation

Apply vendor-supplied patches for Microsoft Defender immediately; until then, minimize network exposure of systems running Defender and monitor for suspicious Defender process behavior.

Recommended fix High confidence

Malware Protection Engine version 1.1.26040.8 or later

  1. Open Windows Security by selecting the shield icon in the task bar or searching for 'Windows Security' in the start menu
  2. Navigate to 'Settings' > 'About' or check the Malware Protection Engine version via: mpcmdrun -getengine
  3. Verify current version is below 1.1.26040.8
  4. Run Windows Update to receive the latest security updates, or manually update Microsoft Defender by opening Windows Security > Virus & threat protection > Check for updates
  5. Restart the device if prompted to complete the update
  6. Confirm the Malware Protection Engine version is now 1.1.26040.8 or higher using: mpcmdrun -getengine
Caveat Microsoft Defender updates are delivered through standard Windows Update and typically have no breaking changes

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Malware Protection Engine Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,760
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,616.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-45584 in production — separate from our analysis above.

No notes yet

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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