Heap buffer overflow via stale gzwrite pointer
Published Sep 3, 2026 · Updated Sep 3, 2026
Heap buffer overflow in zlib 1.3.1.2 through 1.3.2 allows attackers to corrupt memory via formatted writes after a non-blocking stall. gz_vacate passes the remaining byte count and a stale external next_in pointer to memmove without ensuring the copy fits the internal input buffer. The calling application must use gzprintf() or gzvprintf() on a non-blocking destination that stalls, after which the overwrite can corrupt or crash its process.
Summary
What happened
Heap buffer overflow in zlib 1.3.1.2 through 1.3.2 allows attackers to corrupt memory via formatted writes after a non-blocking stall. gz_vacate passes the remaining byte count and a stale external next_in pointer to memmove without ensuring the copy fits the internal input buffer. The calling application must use gzprintf() or gzvprintf() on a non-blocking destination that stalls, after which the overwrite can corrupt or crash its process.
The record
- CVE
- CVE-2026-85091
- Published
- Sep 3, 2026
- Updated
- Sep 3, 2026
- Vendor
- libwww-perl
- Product
- zlib
- Classifications
- Unavailable
- Attack vector
- Unavailable
- Privileges
- Unavailable
Timeline
How it unfolded
- Sep 3, 2026CVE publishedPublication date reported by the CVE source.
- Sep 3, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=1.3.1.2 <=1.3.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
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Public exploit references
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Technologies
Your stack
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Your stack
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