CVE-2026-85091 zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate
Attackers can trigger a heap buffer overflow in zlib via specific gzwrite operations, potentially leading to code execution or denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-85091?
CVE-2026-85091 is a high-severity memory corruption vulnerability in zlib, published on 3 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-787
Which versions are affected by CVE-2026-85091?
How do I fix CVE-2026-85091?
Upgrade to a fixed version.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-85091 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-85091 exists.
Sources
Also known as ALPINE-CVE-2026-85091, AZL-99090, AZL-99174, AZL-99234, AZL-99276, AZL-99294 and 9 more.