High 7.4Published Sep 3, 2026

CVE-2026-85091zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate

Updated under an hour ago (2026-10-19 09:50 UTC)

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Exploited in the last 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.

CVSS: 7.4 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H
Weakness (CWE): CWE-787
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: VulnCheck
NVD analysis: Awaiting Analysis
Record last updated: Sep 3, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

zlib zlib zlib:zlib (from the name)	from 1.3.1.2 through 1.3.2	CNA record

References

https://gist.github.com/thesmartshadow/e0b9481792afb7c31e86fee1ff084490technical-description, exploit
https://github.com/madler/zlib/blob/v1.3.2/gzwrite.c#L393technical-description
https://github.com/madler/zlibproduct
https://www.vulncheck.com/advisories/zlib-1.3.1.2-through-1.3.2-heap-buffer-overflow-via-gz-vacatethird-party-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.