CVE-2026-45498

Description

Microsoft Defender Denial of Service Vulnerability

Overview

State: PUBLISHED
Assigner (CNA): microsoft
CVSS severity: MEDIUM
CVSS score: 4.0 / 10
CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:U/RL:O/RC:C
Effective score: 4.0 / 10 MEDIUM source: CNA overview
MSRC score: 4.0 / 10 MEDIUM MS rating: Low · Denial of Service
CWE(s): CWE-400
Reserved: 2026-05-12
Published: 2026-05-19 07:00 UTC
Last updated: 2026-05-26 07:00 UTC
Source: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/45xxx/CVE-2026-45498.json
Linked Threat: CVE-2026-45498 — Microsoft Defender: Microsoft Defender Denial of Service 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 Denial of Service 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-2026-45498 ; https://nvd.nist.gov/vuln/detail/CVE-2026-45498
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 13:16:36 UTC
NVD last modified: 2026-05-20 19:05:46 UTC
NVD CVSS v3.1: 4.0 / 10 MEDIUM source: secure@microsoft.com
NVD CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Exploitability subscore: 2.5 / 10
Impact subscore: 1.4 / 10
EPSS score: 0.0372 (probability of exploitation in next 30 days)
EPSS percentile: 88.13% 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-2026-31102
Assigner: microsoft
Published: May 20, 2026, 1:09:12 PM
Updated: May 27, 2026, 6:37:28 PM
EUVD base score (CVSS 3.1): 4.0 / 10
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:U/RL:O/RC:C
EUVD-reported EPSS: 4.1100
Vendors: Microsoft
Products: Microsoft Defender Antimalware Platform (4.0.0.0 <4.18.26040.7)

Microsoft Defender Antimalware Platform (-)
Aliases: GHSA-8gp3-pghr-6wxp

ENISA description: Microsoft Defender Denial of Service Vulnerability

EUVD references (1)

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45498

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: Low
Impact: Denial of Service
MS CVSS base score: 4.0 / 10 (temporal 3.5)
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/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 4.18.26040.7)
https://www.microsoft.com/en-us/wdsi/defenderupdates — None Available / Release Notes

Microsoft FAQ (1)

References	Identification
Last version of the Microsoft Defender Antimalware Platform affected by this vulnerability	4.18.26030.3011
First version of the Microsoft Defender Antimalware Platform with this vulnerability addressed	Version 4.18.26040.7

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 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.

How often are the Microsoft Defender Antimalware Platform and malware definitions updated?

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.

What is the Microsoft Defender Antimalware Platform?

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.

Microsoft Defender uses the Windows Defender Antimalware Platform. On which products is Defender installed and active by default?

Defender runs on all supported versions of Windows.

Are there other products that use the Microsoft Defender Antimalware Platform?

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.

Suggested Actions

Verify that the update is installed

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.

Affected products (1)

Vendor	Product	Versions	Platforms
Microsoft	Microsoft Defender Antimalware Platform	`-` (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:defender_antimalware_platform:*:*:*:*:*:*:*:*

Vendor references (1)

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

Microsoft Defender Denial of Service Vulnerability vendor-advisorypatch

Web references (17)

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-2026-45498 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-2026-45498 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://deadeclipse666.blogspot.com/2026/04/funny-dos-tool.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-2026-45498 tenable:msrc.microsoft.com
https://nvd.nist.gov/vuln/detail/CVE-2026-45498 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-2026-45498 secure@microsoft.com Vendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-45498 134c704f-9b21-4f2e-91b3-4a467353bcc0 Third Party AdvisoryUS Government Resource

Indicators (1)

IOCs linked to the auto-promoted Threat row.

Type	Value	VirusTotal	Attached
cve	`CVE-2026-45498`	no local data	2026-05-20 22:08 UTC

Remediations (18)

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

CVE-2026-45498 - Vulnerability Details - OpenCVE

web:app.opencve.io

Remediation No vendor fix or workaround currently provided. OpenCVE Recommended Actions Apply the latest Defender update published by Microsoft via the update guide linked in the advisory. Configure Defender to restrict file scanning of untrusted content, disabling or limiting external drive scans where not needed to reduce exposure to ...

2026-05-24 12:01 UTC
CVE-2026-41091 & CVE-2026-45498: Microsoft Defender Zero-Days Under ...

web:colibrisec.org

CISA added two Microsoft Defender zero-days to its Known Exploited Vulnerabilities catalog on May 20, 2026 , with a June 3 federal remediation deadline. Both CVE - 2026 -41091 (local privilege escalation to SYSTEM) and CVE-2026-45498 (denial of service) are confirmed actively exploited in the wild.

2026-05-24 12:01 UTC
CVE-2026-45498 | Medium | CVETodo

web:cvetodo.com

The best mitigation is to promptly apply the latest security patches provided by Microsoft, restrict local access, and monitor systems for unusual behavior. For detailed patch information and updates, refer to: Microsoft Security Update Guide - CVE-2026-45498 If you need further analysis or assistance with specific environments, please let me know!

2026-05-24 12:01 UTC
Microsoft Defender, Denial of Service, CVE-2026-45498 (Medium)

web:dailycve.com

Prediction: Patch released 2026 -05-20 Analytics What Undercode Say: This vulnerability is significant as it disables the first line of defense on Windows systems. The immediate availability of a patch (version 4.18.26040.7) and its inclusion in CISA's KEV catalog, with a remediation deadline of June 3, 2026 , indicate a high operational risk.

2026-05-24 12:01 UTC
Microsoft Defender RedSun/UnDefend CVE Patch Guide

web:fixitphill.com

CISA KEV patch guide for Microsoft Defender CVE - 2026 -41091 and CVE-2026-45498 on Windows Server, hosting, RDS, Hyper-V, and admin machines.

2026-05-24 12:01 UTC
Nvd - Cve-2026-45498

web:nvd.nist.gov

Information Technology Laboratory National Vulnerability Database Vulnerabilities

2026-05-24 12:01 UTC
Microsoft Defender CVE-2026-41091 & CVE-2026-45498

web:thecyberexpress.com

Microsoft confirms active exploitation of CVE - 2026 -41091 and CVE-2026-45498 in Defender, with CVSS-rated risks, KEV listing, and urgent patches issued.

2026-05-24 12:01 UTC
CVE-2026-41091 and CVE-2026-45498: Microsoft Defender Flaws Actively ...

web:vulert.com

Microsoft warns that two Defender vulnerabilities, CVE - 2026 -41091 and CVE-2026-45498 , are actively exploited. Learn impact, fixed versions, update steps, and how Vulert can help.

2026-05-24 12:01 UTC
Microsoft Defender Zero‑Days Patched May 20: CVE‑2026‑41091 and CVE ...

web:www.studioglobal.ai

What are the key points to validate first? Microsoft released an out‑of‑band Defender update on May 20, 2026 to fix two zero‑day vulnerabilities—CVE‑2026‑41091 (privilege escalation via link‑following) and CVE‑2026‑45498 (denial of service)—both confirmed as a...

2026-05-24 12:01 UTC
CVE-2026-45498 — MEDIUM Vulnerability | CISA KEV | CVSS 4.0 | ThreatClaw

web:www.threatclaw.ai

ThreatClaw assigns CVE-2026-45498 an exploitation risk score of 50/100 with medium confidence. CVE-2026-45498 scores 50/100 driven by confirmed active exploitation (CISA KEV). Given this profile, prompt remediation is warranted for affected systems. Schedule patching within your next maintenance window and monitor for IOCs.

2026-05-24 12:01 UTC
Patch Tuesday May 2026: Security Updates & CVE Analysis

web:zecurit.com

Get the complete breakdown of Microsoft's May 2026 Patch Tuesday. We analyze the latest security updates and all critical CVEs .

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
Microsoft Defender, Denial of Service (DoS), CVE-2026-45498 (Medium ...

web:dailycve.com

CVE-2026-45498 is a Medium‑severity Denial‑of‑Service vulnerability in the Microsoft Defender Antimalware Platform. The root cause lies in insufficient input validation within the core scanning engine.

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-2026-45498 - Microsoft Defender Denial of Service Vulnerability

web:www.scyscan.com

Vulnerability Name Microsoft Defender Denial of Service Vulnerability Description Microsoft Defender contains an unspecified vulnerability that allows for denial of service. Known To Be Used in Ransomware Campaigns? Unknown 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 ...

2026-05-20 22:08 UTC
CVE-2026-45498 - Medium Vulnerability - TheHackerWire

web:www.thehackerwire.com

CVE-2026-45498 is a Medium severity vulnerability (CVSS 4). Microsoft Defender Denial of Service Vulnerability

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

Only Available for Registered Users. Sign in to view.

Raw JSON

The full cvelistV5 record. Download as CVE-2026-45498.json.

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