CVE-2026-33825
CVE-2026-33825 is a security flaw in Microsoft Defender, the antivirus built into Windows. Someone who already has a foothold can use Microsoft Defender to take full control of the machine. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 22 Apr 2026, and says ransomware gangs have used it.[1]
Microsoft Defender is in things households have, such as phones, computers, browsers and everyday apps, so the fix matters at home as much as at work. Fixed in version 4.18.26030.3011 of Microsoft Defender Antimalware Platform.
Description
CISA calls it an insufficient granularity of access control in Microsoft Defender. In its words: “Microsoft Defender contains an insufficient granularity of access control vulnerability that could allow an authorized attacker to escalate privileges locally.”[1]
The underlying weakness is CWE-1220, in MITRE’s list of common software weaknesses.[2]
It scores 7.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by the organisation that published the CVE using CVSS 3.1.[2]
Affected versions
NVD’s record lists one fixed version: everything before it is affected.[2]
| Product | Fixed in |
|---|---|
| Microsoft Defender Antimalware Platform | 4.18.26030.3011 |
Every device with Microsoft Defender needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 22 Apr 2026, 8 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 6 May 2026 to fix it.[1] CISA says ransomware gangs have used it.
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 7%. That’s in the top 7% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Microsoft has published a fix or advice.[3] CISA’s 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.”[1]
- Update Microsoft Defender now.Install the latest update from Microsoft on every device that has it, and restart when asked. Then turn on automatic updates, so the next fix arrives on its own.
- Check you’re on 4.18.26030.3011 or later.Fixed in version 4.18.26030.3011 of Microsoft Defender Antimalware Platform. Anything older is what attackers are going after.
- If there’s no update, stop using it.CISA’s advice when a flaw being used in attacks has no fix is to stop using the product until it does.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 7.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 7%.[4] |
See also
Other Microsoft Defender flaws
- CVE-2026-45498: denial of service ·
- CVE-2026-41091: link following ·
- CVE-2022-44698: smartScreen security feature bypass ·
- CVE-2021-1647: remote code execution ·
Other Microsoft flaws
- CVE-2026-96951, Microsoft Windows: command injection ·
- CVE-2026-65660, Microsoft SharePoint: code injection ·
- CVE-2026-85880, Microsoft Windows: heap-based buffer overflow ·
- CVE-2026-81963, Microsoft Windows: link following ·
- CVE-2019-1068, Microsoft SQL Server: remote code execution ·
Similar flaws
- CVE-2025-31201, Apple devices: arbitrary read and write ·
Every Microsoft flaw on CISA’s list · Everything added in April 2026
References
- ^ Cybersecurity and Infrastructure Security Agency. “Microsoft Defender Insufficient Granularity of Access Control Vulnerability”. Known Exploited Vulnerabilities Catalog, added 22 Apr 2026.
- ^ National Institute of Standards and Technology. “CVE-2026-33825 Detail”. National Vulnerability Database, published 14 Apr 2026.
- ^ Microsoft. Advisories and fixes: msrc.microsoft.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.067, percentile 94.0, 31 Oct 2026.
- CVE Program. “CVE-2026-33825”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.