CVERadar
HIGH · CVSS 3.1 7.5CISA KEV · added 2026-05-20EPSS 1.27% (p70)Threat level 53

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

Microsoft · Defender · NVD published 2026-05-20 · posted 2026-05-20 · last modified 2026-07-23

What it is

Microsoft Defender Denial of Service Vulnerability

WeaknessCWE-400
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (source: [email protected])
CISA due date2026-06-03 (for US federal agencies under BOD; a good deadline for everyone)
ATT&CK tacticsImpact

Exploitation evidence

First exploit evidence seen: 2026-05-20 (earliest date across the sources below).

Exploited in the wild

  • CISA KEV: listed since 2026-05-20. Source

Public exploit code

GitHub proof-of-concept repositories below quality bar

1 public repositories from 1 accounts, first seen 2026-07-02.

Verify before running: public PoCs can be malicious. Read the code and only run it in an isolated lab. A PoC means exploit code is public, not that this CVE is exploited in the wild.

Sources: CISA KEV · nomi-sec/PoC-in-GitHub.

Defend the Chain

The attack chain for CVE-2026-45498 laid across the MITRE ATT&CK Enterprise tactics. Solid cards come from the MITRE CTID KEV mappings; dashed cards are inferred by CVERadar from the CWE or description. Correct defences are real ATT&CK mitigations for that technique.

Threat level 53/100
Defender level 1 · 0 XP
Chain links broken: 0/1

Reconnaissance

Resource Development

Initial Access

Execution

Persistence

Privilege Escalation

Stealth

Defense Impairment

Credential Access

Discovery

Lateral Movement

Collection

Command and Control

Exfiltration

Impact

Pick a red technique card on the board, then choose the defence that stops it.

Defend against T1499 Endpoint Denial of Service Inferred

Inferred from CWE CWE-400

How to fix it

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. (source: CISA KEV)

Fixed versions

  • microsoft defender antimalware platform: upgrade to 4.18.26040.7 or later

Derived from the NVD CPE configuration (versionEndExcluding / versionEndIncluding). Always confirm with the vendor advisory.

Vendor advisories and patches

MITRE ATT&CK mitigations for this chain

  • M1037 Filter Network Traffic (for T1499) : Leverage services provided by Content Delivery Networks (CDN) or providers specializing in DoS mitigations to filter traffic upstream from services. Filter boundary traffic by blocking source addresses sourcing the attack, blocking ports that are being targeted, or blocking protocols being used for transport. To defend

Detection Generic guidance

  • Impact: Monitor service availability, unexpected encryption activity and mass file changes.

Response checklist Generic guidance

  1. Inventory: find every instance of the affected product and version (include internet-facing and forgotten ones).
  2. Patch or mitigate per the vendor advisory; if you cannot patch, remove internet exposure or apply the vendor workaround.
  3. Assume compromise if the system was exposed before patching: hunt for the indicators in the advisory and review logs back to the disclosure date.
  4. Rotate credentials and secrets stored on or used by the affected system if compromise cannot be ruled out.

Sources