CVE-2026-45498: Microsoft Defender Denial of Service Vulnerability — Fixed versions

Summary

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

Remediation

Inventory every Microsoft Defender deployment, including staging.
Upgrade Microsoft Defender to 4.18.26040.7.
Confirm the running version after the upgrade.
Review logs from before the change for signs of exploitation.

CISA required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

References

Patchhttps://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45498
Advisoryhttps://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-45498
Advisoryhttps://nvd.nist.gov/vuln/detail/CVE-2026-45498
Referencehttps://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-45498