CVE-2026-27820

9.8 CRITICAL

zlib is a Ruby interface for the zlib compression/decompression library

Published: 2026-04-16 · Last updated: 2026-05-21

Severity and scoring

CVSS: 9.8 CRITICAL
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CWE: CWE-120, CWE-131

Affected products

Vendor	Product
ruby-lang	zlib

Description

zlib is a Ruby interface for the zlib compression/decompression library. Versions 3.0.0 and below, 3.1.0, 3.1.1, 3.2.0 and 3.2.1 contain a buffer overflow vulnerability in the Zlib::GzipReader. The zstream_buffer_ungets function prepends caller-provided bytes ahead of previously produced output but fails to guarantee the backing Ruby string has enough capacity before the memmove shifts the existing data. This can lead to memory corruption when the buffer length exceeds capacity. This issue has been fixed in versions 3.0.1, 3.1.2 and 3.2.3.

Source: NVD

References

[NVD]https://nvd.nist.gov/vuln/detail/CVE-2026-27820
[Vendor advisory]https://github.com/ruby/zlib/security/advisories/GHSA-g857-hhfv-j68w
[Other]https://hackerone.com/reports/3467067

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