CVE-2026-27820

CVE Details

Release Date:	2026-04-16
Impact:	Moderate	What is this?

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.

See more information about CVE-2026-27820 from MITRE CVE dictionary and NIST NVD

NOTE: The following CVSS metrics and score provided are preliminary and subject to review.

CVSS v3 metrics

Base Score:	5.6
Vector String:	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
Version:	3.1
Attack Vector:	Network
Attack Complexity:	High
Privileges Required:	None
User Interaction:	None
Scope:	Unchanged
Confidentiality Impact:	Low
Integrity Impact:	Low
Availability Impact:	Low

Errata information

Platform	Errata	Release Date
Oracle Linux version 8 (ruby)	ELSA-2026-50728	2026-08-10
Oracle Linux version 8 (rubygem-abrt)	ELSA-2026-50728	2026-08-10
Oracle Linux version 8 (rubygem-mysql2)	ELSA-2026-50728	2026-08-10
Oracle Linux version 8 (rubygem-pg)	ELSA-2026-50728	2026-08-10
Oracle Linux version 9 (ruby)	ELSA-2026-50827	2026-08-10
Oracle Linux version 9 (ruby)	ELSA-2026-50828	2026-08-07
Oracle Linux version 9 (rubygem-mysql2)	ELSA-2026-50827	2026-08-10
Oracle Linux version 9 (rubygem-mysql2)	ELSA-2026-50828	2026-08-07
Oracle Linux version 9 (rubygem-pg)	ELSA-2026-50827	2026-08-10
Oracle Linux version 9 (rubygem-pg)	ELSA-2026-50828	2026-08-07