Description
zlib 1.2.11 through 1.3.2 contains a heap buffer overflow: after an underlying write() fails, gz_write() returns without resetting strm.next_in, leaving it pointed at the caller's buffer. A later gz* write call then derives a position from the stale pointer and writes past a heap allocation; any write() failure reaches it, including EPIPE on a blocking descriptor, and in versions before 1.3.1.2 the failed write must be followed by a gzclearerr() call.
Published: 2026-09-03
Score: 8.3 High
EPSS: < 1% Very Low
KEV: No
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Remediation

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Tracking

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Advisories
Source ID Title
Ubuntu USN Ubuntu USN USN-8954-1 zlib vulnerability
History

Fri, 13 Nov 2026 14:30:00 +0000

Type Values Removed Values Added
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. zlib 1.2.11 through 1.3.2 contains a heap buffer overflow: after an underlying write() fails, gz_write() returns without resetting strm.next_in, leaving it pointed at the caller's buffer. A later gz* write call then derives a position from the stale pointer and writes past a heap allocation; any write() failure reaches it, including EPIPE on a blocking descriptor, and in versions before 1.3.1.2 the failed write must be followed by a gzclearerr() call.
Title zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate zlib 1.2.11 through 1.3.2 Heap Buffer Overflow via Stale gzwrite Pointer After Failed Write
References

Thu, 03 Sep 2026 14:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Thu, 03 Sep 2026 01:15:00 +0000

Type Values Removed Values Added
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.
Title zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate
First Time appeared Zlib
Zlib zlib
Weaknesses CWE-787
CPEs cpe:2.3:a:zlib:zlib:*:*:*:*:*:*:*:*
Vendors & Products Zlib
Zlib zlib
References
Metrics cvssV3_1

{'score': 7.4, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H'}

cvssV4_0

{'score': 8.3, 'vector': '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'}


cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-11-13T14:15:55.362Z

Reserved: 2026-09-02T23:53:05.582Z

Link: CVE-2026-85091

cve-icon Vulnrichment

Updated: 2026-09-03T13:21:22.797Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-09-03T13:06:20.573

Modified: 2026-11-13T15:17:56.490

Link: CVE-2026-85091

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-03T10:30:12Z

Weaknesses