CVE-2026-27820
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.
Does this matter?
Lower severity and a low EPSS score (0.56%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 4.0
- 1.7 LOWCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.56% probability · 45th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-120, CWE-131
- Affected
- ruby-lang/zlib
- Source
- security-advisories@github.com
References
- https://github.com/ruby/zlib/security/advisories/GHSA-g857-hhfv-j68wVendor Advisory
- https://hackerone.com/reports/3467067Permissions Required
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.