---
title: "CVE-2026-45498: Microsoft Defender Denial of Service Vulnerability"
url: https://erroneo.us/security/cve/CVE-2026-45498/
description: "CVE-2026-45498 (Microsoft Defender): Exploited in the wild (CISA KEV). Microsoft Defender Denial of Service Vulnerability"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-05-20
date_modified: 2026-08-10
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-45498"
kev: true
cvss: 4
epss: 0.01267
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-45498: Microsoft Defender Denial of Service Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run Microsoft Defender. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-05-20, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-06-03 ; treat that as the outer limit, not the target.
- EPSS 1.3% , percentile 70: FIRST’s model estimates a 1.3% chance of exploitation activity in the next 30 days, higher than 70% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Needs local access needed. Lower urgency for most teams unless an attacker could already run code on the machine.

## What it is

Microsoft Defender Denial of Service Vulnerability

## Affected products (CVE record)

- Microsoft Microsoft Defender Antimalware Platform: 4.0.0.0 < 4.18.26040.7

## Severity

- microsoft CVSS 3.1: 4 `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`

## Exploitation

- CISA KEV: added 2026-05-20; federal due date 2026-06-03. Known ransomware use: Unknown.
- CISA 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.
- CISA SSVC assessment: exploitation active , automatable no , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 1.27% probability of exploitation activity in the next 30 days; percentile 70.

## Sources

- [Microsoft Defender Denial of Service Vulnerability](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45498)
- [Listed in CISA KEV notes (msrc.microsoft.com)](https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-45498)
- [CVE.org record CVE-2026-45498](https://www.cve.org/CVERecord?id=CVE-2026-45498)
- [NVD entry CVE-2026-45498](https://nvd.nist.gov/vuln/detail/CVE-2026-45498)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-45498)

---
Source page: https://erroneo.us/security/cve/CVE-2026-45498/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt