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Exploited vulnerability · CISA KEV

Is CVE-2026-45498 exploited? Yes: in CISA KEV since 20 May 2026

Gociux · Microsoft Defender · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2026-45498, Microsoft Defender Denial of Service Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 20 May 2026, the day it was published. It affects Microsoft Defender. If you run it, CISA's required action is: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

exploitedYesCISA KEV · 20 May 2026
ransomwareNot knownno confirmed use
EPSStop 1%among the most likely CVEs to be exploited
severity4CVSS 3.1 · medium
US federal due3 Jun 2026BOD 22-01 deadline

What it is

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

VendorMicrosoft (391 exploited CVEs in KEV)
ProductDefender
VulnerabilityMicrosoft Defender Denial of Service Vulnerability
Weaknessnot specified
Published20 May 2026
Added to KEV20 May 2026
Reported by (CNA)microsoft

What to do

  1. Check whether you run it. Look for Defender in your asset inventory, including appliances and cloud images. Stack check lists every exploited Microsoft CVE at once.
  2. Apply the fix. Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
  3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 20 May 2026.
  4. Get told next time. Email alerts when CISA adds a CVE for Microsoft.

Other exploited CVEs in Defender

References

Questions

Is CVE-2026-45498 being exploited?

Yes. CISA added CVE-2026-45498 to the Known Exploited Vulnerabilities catalog on 20 May 2026, which means there is reliable evidence of exploitation in the wild.

Is CVE-2026-45498 used in ransomware attacks?

CISA does not list known ransomware use for it. That can change, and exploitation alone is reason to fix it first.

How do I fix CVE-2026-45498?

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Check Microsoft's advisory for the fixed versions, and if you can't patch quickly, restrict access to the affected Defender and watch it for signs of compromise.

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in May 2026 · Microsoft scorecard · act-now radar.

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