CVE-2026-85091
Published: September 8, 2026Last modified: October 2, 2026
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.
Severity score breakdown
| Parameter | Value |
|---|---|
| Base score | 7.4 |
| Attack Vector | NETWORK |
| Attack complexity | HIGH |
| Privileges required | NONE |
| User interaction | NONE |
| Scope | UNCHANGED |
| Confidentiality | NONE |
| Integrity impact | HIGH |
| Availability impact | HIGH |
| Vector | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H |
Status
| Product | Release | Package | Status |
|---|---|---|---|
| Alpaquita Linux | 23 LTS | zlib | Not affected (1.2.13-r0) |
| 25 LTS | zlib | Fixed (1.3.2-r1) | |
| Stream | zlib | Fixed (1.3.2-r1) | |
| Hardened Containers | 23 LTS | zlib | Not affected (1.2.13-r0) |
| 25 LTS | zlib | Fixed (1.3.2-r1) | |
| Stream | zlib | Fixed (1.3.2-r1) |
References
- https://gist.github.com/thesmartshadow/e0b9481792afb7c31e86fee1ff084490
- https://github.com/madler/zlib
- https://github.com/madler/zlib/blob/v1.3.2/gzwrite.c#L393
- https://www.vulncheck.com/advisories/zlib-1.3.1.2-through-1.3.2-heap-buffer-overflow-via-gz-vacate
- https://github.com/madler/zlib/commit/df84af25dc1942490e1d1c899a07619152a46148