What is CVE-2026-55011?
Integer underflow (wrap or wraparound) in Microsoft Defender allows an unauthorized attacker to execute code locally.
The record classifies CVE-2026-55011 under weakness class CWE-191. Its CVSS v3 base vector states that the flaw requires local access to the host, needs no prior authentication, needs a user to take an action first, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 106 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 7.8 — HIGH
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C - EPSS (FIRST)
- 0.4% probability of exploitation in the next 30 days, higher than 38.4% of all scored CVEs
- CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 5.4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-07-14, last modified 2026-10-08
Is CVE-2026-55011 being exploited?
It currently carries a trending score of 33 in the Threadlinqs vulnerability feed.
Affected products and versions
- Microsoft: Malware Protection Engine
How to fix CVE-2026-55011
No vendor patch reference has been recorded for CVE-2026-55011 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.
Threat activity tracking CVE-2026-55011
3 tracked threats in the Threadlinqs corpus reference CVE-2026-55011, either in the campaign’s CVE list or as an indicator on the campaign record.
- Microsoft July 2026 Patch Tuesday: 570 Flaws Fixed, 3 Zero-Days Including AD FS and SharePoint Privilege Escalation — CRITICAL · 2026-07-14
- Microsoft July 2026 Patch Tuesday: 570 Vulnerabilities Fixed, Including 2 Actively Exploited Zero-Days (CVE-2026-56164, CVE-2026-56155) — CRITICAL · 2026-07-14
- Microsoft July 2026 Patch Tuesday: Record 622 CVEs Include Two Actively Exploited Zero-Days in AD FS (CVE-2026-56155) and SharePoint Server (CVE-2026-56164) — CRITICAL · 2026-07-14
Sources
Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on .