CVE-2026-85091: Zlib

High severity, CVSS 7.4. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• Zlib Zlib: from 1.3.1.2, up to and including 1.3.2

Published 2026-09-03. Last modified 2026-09-09.