22 May 2026
Reference: CVE-2026-45498
1. What is being reported?
Researchers have found a weakness in Microsoft Defender, a common security program, that could let attackers cause a denial of service. This means the software could be overwhelmed or stopped from running, potentially leaving your devices unprotected.
2. What this means in plain English
If Microsoft Defender stops working because of this vulnerability, your devices might not be protected against other cyber threats. This could increase the risk of malware infections or other attacks that could disrupt your business operations.
3. Could this affect a small business?
Small businesses using Microsoft Defender on their computers or servers could be affected, especially if they rely on it for security. Organisations not using this product or using alternative security solutions are less likely to be impacted.
4. What to do now
- Check with your IT provider or software supplier if updates or mitigations are available for Microsoft Defender.
- Apply any recommended updates or mitigations from Microsoft as soon as possible.
- Follow any additional guidance provided for cloud services if you use Microsoft Defender in the cloud.
- If no mitigation is available, consider temporarily discontinuing use of Microsoft Defender until the issue is resolved.
5. Ask your IT provider
Can you confirm if our Microsoft Defender software is affected by CVE-2026-45498 and what steps have been taken to protect us from this vulnerability?
6. Bottom line
Act promptly to ensure Microsoft Defender is updated or mitigated to keep your devices protected.
Information based on CISA KEV, NVD and reputable security reporting.