Security Digest · Vulnerability record · Known exploited
CVE-2026-41091: Microsoft Defender Link Following Vulnerability
Exploited in the wild (CISA KEV). Improper link resolution before file access ('link following') in Microsoft Defender allows an authorized attacker to elevate privileges locally.
CISA KEV · added 2026-05-20 CVSS 7.8 High EPSS 0.4% · p37
Should you act?
Exploited: patch now if you run it
CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- Yes, if you run Microsoft Defender. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-05-20, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-06-03; treat that as the outer limit, not the target.
- EPSS 0.4%, percentile 37: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 37% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Needs local access needed. Lower urgency for most teams unless an attacker could already run code on the machine.
What it is
Improper link resolution before file access ('link following') in Microsoft Defender allows an authorized attacker to elevate privileges locally.
CISA’s summary
Microsoft Defender contains a link following vulnerability that allows an authorized attacker to elevate privileges locally.
Weakness type: CWE-59.
Product: Microsoft Defender · Assigned by: microsoft · Published: 2026-05-20
Affected and fixed versions
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| Microsoft | Microsoft Malware Protection Engine | 1.1.0.0 < 1.1.26040.8 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| microsoft | 3.1 | 7.8 High | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C |
- Attack vector: local access needed
- Attack complexity: low
- Privileges required: low (any account)
- User interaction: none
- Scope: unchanged
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: added 2026-05-20; federal due date 2026-06-03. Known ransomware use: Unknown.
- 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 SSVC assessment: exploitation active, automatable no, technical impact total.
- FIRST EPSS (model of 2026-10-21): 0.44% probability of exploitation activity in the next 30 days; percentile 37.
Timeline
- — Added to CISA’s Known Exploited Vulnerabilities catalog
- — CVE record published by microsoft
- — CISA remediation deadline for US federal agencies
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vendor and project advisories, patches
- Microsoft Defender Elevation of Privilege Vulnerability msrc.microsoft.com
- Listed in CISA KEV notes (msrc.microsoft.com) msrc.microsoft.com
Vulnerability records
- CVE.org record CVE-2026-41091 cve.org
- NVD entry CVE-2026-41091 nvd.nist.gov
Government
All exploited Microsoft vulnerabilities · Today’s Security Digest