CVE-2026-85091
zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate
CVSS Score
7.4
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-787 |
| Vendor | zlib |
| Product | zlib |
| Published | Sep 3, 2026 |
| Last Updated | Sep 3, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
High
Affected Versions
zlib / zlib
1.3.1.2 ≤ 1.3.2
References
gist.github.com: https://gist.github.com/thesmartshadow/e0b9481792afb7c31e86fee1ff084490 github.com: https://github.com/madler/zlib/blob/v1.3.2/gzwrite.c#L393 github.com: https://github.com/madler/zlib vulncheck.com: https://www.vulncheck.com/advisories/zlib-1.3.1.2-through-1.3.2-heap-buffer-overflow-via-gz-vacate
Credits
Ali Firas (thesmartshadow)