Vulnerability report

Exploited in the wild Confirmed confidence In CISA KEV

CVE-2026-45498

Microsoft Defender Denial of Service Vulnerability

Microsoft Defender Antimalware Platform · affected before 4.18.26040.7

Watch CVE-2026-45498 Browse KEV feed
Severity
CVSS 4.0 · Medium
Confidence
Confirmed
Exploit status
Exploited in the wild
EPSS
1.3%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2026-45498 is an unauthenticated Microsoft Defender Denial of Service Vulnerability.

Is it exploited?

Yes. Previdian tracks this CVE as a known exploited vulnerability. Confidence is confirmed. Listed in CISA KEV. Also confirmed by third-party sources.

Who is affected?

Microsoft Defender Antimalware Platform affected before 4.18.26040.7.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

Microsoft Defender Denial of Service Vulnerability

Microsoft Defender Denial of Service Vulnerability

Microsoft Affected
Microsoft Defender Antimalware Platform
Before 4.18.26040.7
View vendor advisory (opens in new tab)
Published
20 May 2026
Exploitation Reported
01 Jun 2026
Attack vector
Local
Complexity
Low
Privileges
None
User interaction
None

Tags

cisa microsoft

CVE References

Exploitation evidence

Why Previdian marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CVE

Recorded 01 Jun 2026

A trusted third party reported exploitation.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

Learn about Pro API access
Source Added
CVE First 2026-06-01 13:29 UTC
CISA 2026-06-02 14:00 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
User-Agents
Callback hosts
0
0
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Scanner coverage

No scanner integrations recorded yet.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

No detection artifacts or sensor request patterns are available for this CVE yet.

Check back as sensor telemetry and scanner integrations are updated.

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

4.0 Medium

Potential damage if exploited. Separate from whether attackers are using it.

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

EPSS

1.3%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Uncontrolled Resource Consumption CWE-400

Recent mention · The Hacker News

Researcher Drops BigDiskBuster Zero-Day PoC That Blocks Microsoft Defender Updates

Swati KhandelwalSep 22, 2026Vulnerability / Endpoint Security A zero-day proof-of-concept tool that stops Microsoft Defender from installing platform and signature updates by filling all available disk space was published on GitHub on September 19. The tool, called...

Read full advisory

All Mentions

Recent mention · The Hacker News

Researcher Drops BigDiskBuster Zero-Day PoC That Blocks Microsoft Defender Updates

The Hacker News · 22 Sep 2026

Swati KhandelwalSep 22, 2026Vulnerability / Endpoint Security A zero-day proof-of-concept tool that stops Microsoft Defender from installing platform and signature updates by filling all available disk space was published on GitHub on September 19. The tool, called BigDiskBuster, has no patch, no CVE, and no Microsoft advisory. Its author, Abdelhamid Naceri, is a former Microsoft security researcher whose earlier Defender exploits were used in attacks. When updates are blocked, Defender keeps running, but its detection content grows stale. The researcher's screenshot shows Defender...

Recent mention · Rapid7

Patch Tuesday - June 2026

Rapid7 · 09 Jun 2026

Microsoft is publishing 200 vulnerabilities on June 2026 Patch Tuesday. Microsoft is not aware of exploitation in the wild for any of these vulnerabilities, and is aware of public disclosure for three. This is similar to last month’s Patch Tuesday, however several of last month’s vulnerabilities ended up on CISA KEV in the days following their publication. So far this month, Microsoft has provided patches to address 360 browser vulnerabilities, which is an order of magnitude more than has been typical in any given month over the past few years. As usual, browser vulns are not included in...

Timeline

From disclosure to observed exploitation

  1. 14:00 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  2. 13:29 UTC

    Added to Previdian KEV Feed

    High-confidence, third-party attested exploitation

  3. 13:09 UTC

    CVE published

    Vulnerability disclosed publicly

  4. 16:07 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2026-45498

Sample API response 
{
  "cve_id": "CVE-2026-45498",
  "confidence": "Confirmed",
  "cvss_score": 4.0,
  "cvss_estimated": false,
  "epss_score": 0.01267,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}