CVE-2026-33825: Microsoft Defender Insufficient Granularity of Access Control Vulnerability

In short

Microsoft Defender has a weakness classified as CWE-1220. CISA added it to its Known Exploited Vulnerabilities catalog on 2026-04-22. NVD lists CVSS 3.1 at 7.8 HIGH. CISA reports known ransomware campaign use.

What it is

“Microsoft Defender contains an insufficient granularity of access control vulnerability that could allow an authorized attacker to escalate privileges locally.” — CISA KEV, retrieved 2026-11-01

“Insufficient granularity of access control in Microsoft Defender allows an authorized attacker to elevate privileges locally.” — NVD, retrieved 2026-11-01

Who is affected

Microsoft Defender. NVD lists the following versions as affected:

• Versions before 4.18.26030.3011

Exploitation status

CISA KEV added: 2026-04-22. Known ransomware campaign use: Known (reported by CISA). Due date CISA set for US federal civilian agencies: 2026-05-06.

Scores

NVD CVSS 3.1: 7.8 HIGH; vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H; source [email protected].

EPSS by FIRST: 6.75%; percentile 93.97; score date 2026-10-31. EPSS estimates the probability of exploitation in the next 30 days.

CWE: CWE-1220.

Timeline

CISA required action

“Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.” — CISA KEV

What to do

• Confirm whether you run Microsoft Defender and which version.
• Apply the vendor update or mitigation in the advisory.
• Follow CISA’s required action.
• Review the vendor guidance on signs of compromise.
• Track the fix through completion.

References

• Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-33825
• Third Party Advisory: https://www.huntress.com/blog/nightmare-eclipse-intrusion
• NVD detail
• CVE.org record
• CISA KEV catalog

Sources and dates

CISA Known Exploited Vulnerabilities Catalog, version 2026.10.30; retrieved 2026-11-01. CISA KEV data: CC0 1.0. No endorsement by CISA.

NVD retrieved: 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.

EPSS scores by FIRST; score date 2026-10-31.