CVE-2026-27820
Published:April 16, 2026
Updated:April 23, 2026
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.
Affected Packages
https://github.com/ruby/zlib.git (GITHUB):
Affected version(s) >=v3.2.0 <v3.2.3Fix Suggestion:
Update to version v3.2.3https://github.com/ruby/zlib.git (GITHUB):
Affected version(s) >=v0.0.1 <v3.0.1Fix Suggestion:
Update to version v3.0.1https://github.com/ruby/zlib.git (GITHUB):
Affected version(s) >=v3.1.0 <v3.1.2Fix Suggestion:
Update to version v3.1.2zlib (RUBY):
Affected version(s) >=0.0.1 <3.0.1Fix Suggestion:
Update to version 3.0.1zlib (RUBY):
Affected version(s) >=3.1.0 <3.1.2Fix Suggestion:
Update to version 3.1.2zlib (RUBY):
Affected version(s) >=3.2.0 <3.2.3Fix Suggestion:
Update to version 3.2.3Related Resources (6)
Do you need more information?
Contact UsCVSS v4
Base Score:
1.7
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
PRESENT
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
LOW
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
Exploit Maturity
UNREPORTED
CVSS v3
Base Score:
5.3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
LOW
Weakness Type (CWE)
EPSS
Base Score:
0.04
