CVE-2026-85091
zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate
- State
- Published
- Severity
- 8.3 High
- Published
- Sep 3, 2026
- Updated
- Sep 3, 2026
- Reserved
- Sep 2, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 8.3 High | 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 | VulnCheck |
| 3.1 | 7.4 High | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H | VulnCheck |
Weaknesses
- CWE-787 Out-of-bounds Write
Affected Products
| Product | Versions |
|---|---|
zlibzlib |
|
References
- Technical report and proof of concepttechnical-descriptionexploit
- https://github.com/madler/zlib/blob/v1.3.2/gzwrite.c#L393technical-description
- https://github.com/madler/zlibproduct
- VulnCheck Advisory: zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacatethird-party-advisory
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