CVE-2026-45498 Microsoft Defender: software flaw
In plain words: A mistake in the software that attackers have found a way to abuse. Depends on the product — see the description and the vendor advisory.
Confirmed exploited by CISA on · US federal patch deadline Jun 3, 2026
What to do
- Install Microsoft's security update for Defender. If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Keep a list of every internet-facing server you run so nothing is forgotten.
- Patch anything in this catalog first, ahead of normal patch cycles.
- Put admin and file-transfer apps behind a VPN or single sign-on instead of the open internet.
Who is affected
Work IT. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.
What's at risk: Mass data theft and ransomware: a single flaw in a file-transfer or email server has exposed thousands of organisations at once.
The details
- Official name
- Microsoft Defender Denial of Service Vulnerability
- Product
- Microsoft Defender
- CISA description
- Microsoft Defender contains an unspecified vulnerability that allows for denial of service.
- Type of flaw
- Software flaw
- Confirmed exploited
- May 20, 2026
- US federal patch deadline
- Jun 3, 2026
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Answering about CVE-2026-45498 ·
Questions about CVE-2026-45498
Is CVE-2026-45498 being exploited?
Yes. CISA added CVE-2026-45498 to its Known Exploited Vulnerabilities catalog on May 20, 2026, which means there is reliable evidence of real-world attacks.
How do I fix CVE-2026-45498?
Install Microsoft's security update for Defender. If no update exists, follow the vendor's workaround or stop using the product until one ships. Keep a list of every internet-facing server you run so nothing is forgotten.
Am I affected by CVE-2026-45498?
Only if you use Microsoft Defender. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.