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Fencer Vulns
high 7.4

CVE-2026-85091 json

zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate

published 2026-09-03 2 mo ago modified 2026-09-09 1 mo ago also EUVD-2026-70301

cvss
7.4
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 40%
public exploits
0
none known

Summary

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.

Patch / fix

  • zlib Debian 13 1:1.3.dfsg+really1.3.1-1+deb13u1
  • zlib Debian 14 1:1.3.dfsg+really1.3.2-4

debian advisories DEBIAN-CVE-2026-85091

  • zlib Ubuntu 24.04 LTS 1:1.3.dfsg-3.1ubuntu2.3
  • zlib Ubuntu 26.10 1:1.3.dfsg+really1.3.2-3ubuntu1.1
  • zlib Ubuntu 26.04 LTS 1:1.3.dfsg+really1.3.1-1ubuntu3.2

ubuntu advisories UBUNTU-CVE-2026-85091

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • trivy openSUSE Tumbleweed 0.76.0-1.1

opensuse advisories openSUSE-SU-2026:12206-1

  • zlib Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 1.3.2-r1

alpine advisories ALPINE-CVE-2026-85091

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • zlib Azure Linux 3.0 1.3.2-2

azure linux advisories AZL-99090

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-85091 updated cvss 8.1

zlib: zlib: Heap buffer overflow in gz_vacate() allows arbitrary code execution

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
total
Assessed
2 mo ago

Exploit prediction

0.47% chance of exploitation in the next 30 days, higher than 40% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • gist.github.com https://gist.github.com/thesmartshadow/e0b9481792afb7c31e86fee1ff084490 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 8.3 CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N
CNA 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H
CNA 4.0 8.3 CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

  • zlib zlib

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.