---
id: "CVE-2026-45498"
kind: "vulnerability"
aliases: ["CVE-2026-45498"]
title: "microsoft defender antimalware platform: Microsoft Defender Denial of Service Vulnerability"
severity: "high"
cvss: 7.5
epss: null
exploited: true
status: "open"
category: "vendor"
products: [{"name": "Microsoft Defender", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "microsoft defender antimalware platform", "fixed": ["4.18.26040.7"], "affected": "< 4.18.26040.7", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exploited", "microsoft-365", "microsoft-defender", "vendor", "windows"]
not_affected_if: ["non-microsoft-defender-environments"]
published_at: "2026-05-20T00:00:00+00:00"
first_seen_at: "2026-10-23T19:11:51+00:00"
updated_at: "2026-10-23T23:44:51+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-45498", "first_seen_at": "2026-10-23T19:11:51+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-45498", "first_seen_at": "2026-10-23T23:44:51+00:00"}]
---

# microsoft defender antimalware platform: Microsoft Defender Denial of Service Vulnerability

Microsoft Defender contains an unspecified flaw that lets an attacker cause a denial of service. CISA lists it as actively exploited in the wild.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Microsoft Defender affected ? fixed ?
- vendor:microsoft defender antimalware platform affected < 4.18.26040.7 fixed 4.18.26040.7

## Fix

Apply the mitigations per Microsoft's vendor instructions referenced by CISA; the sources do not name a patched version. If mitigations are unavailable, CISA says to discontinue use of the product.

## Timeline

- 2026-10-23T19:11:51+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-45498
- 2026-10-23T23:44:51+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-45498

## From the sources

Microsoft Defender contains an unspecified vulnerability that allows for denial of service.

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_