Critical severity9.8NVD Advisory· Published Apr 16, 2026· Updated May 21, 2026
CVE-2026-27820
CVE-2026-27820
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.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
zlibRubyGems | >= 3.2.0, < 3.2.3 | 3.2.3 |
zlibRubyGems | >= 3.1.0, < 3.1.2 | 3.1.2 |
zlibRubyGems | < 3.0.1 | 3.0.1 |
Affected products
4- osv-coords3 versionspkg:apk/chainguard/trufflerubypkg:gem/zlibpkg:rpm/suse/ruby2.5&distro=SUSE%20Linux%20Enterprise%20Module%20for%20Basesystem%2015%20SP7
< 34.0.1-r0+ 2 more
- (no CPE)range: < 34.0.1-r0
- (no CPE)range: >= 3.2.0, < 3.2.3
- (no CPE)range: < 2.5.9-150700.24.6.1
Patches
Vulnerability mechanics
References
6- github.com/advisories/GHSA-g857-hhfv-j68wghsaADVISORY
- github.com/ruby/zlib/security/advisories/GHSA-g857-hhfv-j68wnvdVendor AdvisoryWEB
- nvd.nist.gov/vuln/detail/CVE-2026-27820ghsaADVISORY
- github.com/rubysec/ruby-advisory-db/blob/master/gems/zlib/CVE-2026-27820.ymlghsaWEB
- hackerone.com/reports/3467067nvdPermissions RequiredWEB
- www.ruby-lang.org/en/news/2026/03/05/buffer-overflow-zlib-cve-2026-27820ghsaWEB
News mentions
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