CVE-2026-85091: zlib Out-of-bounds Write
Vulnerability summary
CVE-2026-85091 is a high (CVSS 8.3) Out-of-bounds Write vulnerability in zlib. EPSS estimates a 0.36% chance of exploitation in the next 30 days, higher than 27.8% of scored vulnerabilities. 1 public exploit is recorded.
Timeline
- 03-09-2026PublishedVulnerability first disclosed.
- 03-09-2026Last modifiedVulnerability information updated.
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 metrics
10 scores · 7 sources · 2 versions- OSV · AlpineEcosystem advisory · calculated8.3HighCVSS: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
- OSV · UbuntuEcosystem advisory · calculated8.3HighCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N
- OSV · DebianEcosystem advisory · calculated8.3HighCVSS: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
- OSV · WolfiEcosystem advisory · calculated8.3HighCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N
- OSV · ChainguardEcosystem advisory · calculated8.3HighCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N
- NVDNIST8.3HighCVSS: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
- OSV · UbuntuEcosystem advisory · calculated7.4HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H
- NVDNIST7.4HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H
EPSS trend
Probability
0.36%
Chance of exploitation in the next 30 days
Percentile
28%
Versus all other CVEs
30-day change
-0.09 pp
From 0.44% on 19-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
1 foundE0B9481792Afb7C31E86Fee1Ff084490
Maturity: poc
Weaknesses
CWE · root causeAffected systems
Chainguard5 products
- minizip< 1.3.2.1_rc20260601-r0
- zlib< 1.3.2.1_rc20260601-r0
- zlib-dev< 1.3.2.1_rc20260601-r0
- zlib-doc< 1.3.3-r0 | < 1.3.2.1_rc20260601-r0
- zlib-static< 1.3.2.1_rc20260601-r0 | < 1.3.3-r0
Wolfi5 products
- minizip< 1.3.2.1_rc20260601-r0
- zlib< 1.3.2.1_rc20260601-r0
- zlib-dev< 1.3.2.1_rc20260601-r0
- zlib-doc< 1.3.3-r0 | < 1.3.2.1_rc20260601-r0
- zlib-static< 1.3.2.1_rc20260601-r0 | < 1.3.3-r0
Ubuntu4 products
- klibcAll versions (No fix recorded)
- rsyncAll versions (No fix recorded)
- zlibAll versions (No fix recorded)
- zsyncAll versions (No fix recorded)
Alpine1 product
- zlib< 1.3.2-r1
Debian1 product
- zlibAll versions (No fix recorded)
Zlib1 product
- zlib≥ 1.3.1.2, ≤ 1.3.2
6 vendors · 17 products
References
10 links- gist.github.com/thesmartshadow/e0b9481792afb7c31e86fee1ff084490Technical DescriptionExploitREPORTEVIDENCE
- www.vulncheck.com/advisories/zlib-1.3.1.2-through-1.3.2-heap-buffer-overflow-via-gz-vacateThird Party AdvisoryREPORTAdvisory
