What’s Vulnerable › Vulnerabilities

CVE-2026-76844: zlib 1.2.11 through 1.3.2 Heap Buffer Overflow via Stale gzwrite Pointer After Failed Write

• Severity: high (CVSS 7.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-24 · updated 2026-10-12
• Weakness: CWE-787

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.

Affected products

• Npm Webpack-Dev-Middleware: from 8.0.0 before 8.3.0; before 7.4.6 — fixed in 8.3.0, 7.4.6
• zlib: from 1.2.11 through 1.3.2

How to fix

Upgrade to a fixed version: Npm Webpack-Dev-Middleware 8.3.0, 7.4.6. Check the vendor advisory for mitigations.

References

• https://gist.github.com/thesmartshadow/e0b9481792afb7c31e86fee1ff084490
• https://github.com/madler/zlib
• https://github.com/madler/zlib/blob/v1.3.2/gzwrite.c#L393
• https://github.com/madler/zlib/commit/df84af25dc1942490e1d1c899a07619152a46148
• https://www.vulncheck.com/advisories/zlib-1.3.1.2-through-1.3.2-heap-buffer-overflow-via-gz-vacate

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