High severity · published Sep 3, 2026
CVE-2026-85091
zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate
7.4
CVSS
0.5%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Confidentiality
None
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 40% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
ZL
zlib · zlib
1.3.1.2 through 1.3.2 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-85091
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-85091
gist.github.com
https://gist.github.com/thesmartshadow/e0b9481792afb7c31e86fee1ff084490
github.com
https://github.com/madler/zlib
github.com
https://github.com/madler/zlib/blob/v1.3.2/gzwrite.c#L393
www.vulncheck.com
https://www.vulncheck.com/advisories/zlib-1.3.1.2-through-1.3.2-heap-buffer-overflow-via-gz-vacate
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