CVE-2026-85091 and is rated High severity with a CVSS score of 7.4. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.
What to do next
Remediation and response
Microsoft Security Response Center guidance
Vendor revision: Oct 17, 2026
Release Notes
Vendor-listed releases
1.3.2-2
CISA KEVNot listedBased on the latest collected catalog
EPSS0.5%Estimated 30-day exploitation probability
Ransomware useNot markedCISA KEV ransomware field
Threat actors0Source-linked actor relationships
Overview
What is CVE-2026-85091?
zlib versions 1.3.1.2 through 1.3.2 contain a heap buffer overflow vulnerability in the gz_vacate() function when processing non-blocking gzwrite() operations with stale external buffer pointers. Attackers can trigger the overflow by calling gzprintf() or gzvprintf() after a write stall, causing an unchecked memmove() to write beyond the internal input buffer boundary.