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Low 1 exploited CVE MSRC-CVE-2026-45498 1 CVE

Microsoft Defender Denial of Service Vulnerability

Published May 19, 2026 · Updated May 26, 2026 · Revision 2

Summary

Impact: Denial of Service. Microsoft rating: Low. Exploited according to Microsoft, publicly disclosed before the fix — Exploitation Detected. Customer action: Required.

Details

Microsoft Defender is disabled in my environment, why are vulnerability scanners showing that I am vulnerable to this issue?
Last version of the Microsoft Defender Antimalware Platform affected by this vulnerability: Last version of the Microsoft Defender Antimalware Platform affected by this vulnerability, 4.18.26030.3011: 4.18.26030.3011, First version of the Microsoft Defender Antimalware Platform with this vulnerability addressed: First version of the Microsoft Defender Antimalware Platform with this vulnerability addressed, Version 4.18.26040.7: Version 4.18.26040.7
See Manage Updates Baselines Microsoft Defender Antivirus for more information.
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.
In response to a constantly changing threat landscape, Microsoft frequently updates malware definitions and the Windows Defender Antimalware Platform. 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 Windows Defender Antimalware Platform 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 Windows Defender Antimalware Platform updates and malware definitions, is working as expected in their environment.
Microsoft typically releases an update for the Microsoft Defender Antimalware Platform 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 platform, 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.
The Microsoft Defender Antimalware Platform is a collection of user-mode binaries (e.g. MsMpEng.exe) and kernel-mode drivers that run on top of Windows to keep devices protected against new and prevalent threats.
Defender runs on all supported versions of Windows.
Yes, Microsoft System Center Endpoint Protection, Microsoft System Center 2012 R2 Endpoint Protection, Microsoft System Center 2012 Endpoint Protection and Microsoft Security Essentials.
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.
Customers should verify that the latest version of the Microsoft Malware Protection Platform and definition updates are being actively downloaded and installed for their Microsoft antimalware products.
Open the Windows Security program. For example, type Security in the Search bar, and select the Windows Security program.
In the navigation pane, select Virus & threat protection.
Then click on Protection Updates in the Virus & threat protection section updates.
Select Check for updates.
In the navigation pane, select Settings, and then select About.
Examine the Antimalware ClientVersion number. The update was successfully installed if the Malware Protection Platform version number or the signature package version number matches or exceeds the version number that you are trying to verify as installed.

Security updates
4.18.26040.7 — https://www.microsoft.com/en-us/wdsi/defenderupdates

Vulnerabilities 1

Revision history

  1. #2

    CWE added. Informational change only.

  2. #1

    Information published.

References