CVE-2026-76844: zlib Out-of-bounds Write

Vulnerability summary

CVE-2026-76844 is a high (CVSS 8.3) Out-of-bounds Write vulnerability in zlib. EPSS estimates a 0.59% chance of exploitation in the next 30 days, higher than 47.5% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 24-08-2026
   PublishedVulnerability first disclosed.
2. 01-10-2026
   Last modifiedVulnerability information updated.

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.

• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.