Fluid Attacks Database

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.

Mitigation

Update Impact

Minimal update. May introduce new vulnerabilities or breaking changes.

Ecosystem	Package	Affected version	Patched versions
debian 14	ruby3.3	=3.3.8-2 \|\| =3.3.8-2.1 \|\| =3.3.8-2.2	-
alpine v3.23	ruby	>=0 <3.4.9-r0	3.4.9-r0
rubygems	zlib	>=3.2.0 <3.2.3 \|\| >=3.1.0 <3.1.2 \|\| >=0 <3.0.1	3.2.3, 3.1.2, 3.0.1
debian 11	ruby2.7	=2.7.4-1 \|\| =2.7.4-1+deb11u1 \|\| =2.7.4-1+deb11u2 \|\| =2.7.4-1+deb11u3 \|\| =2.7.4-1+deb11u4 \|\| =2.7.4-1+deb11u5 \|\| =2.7.5-1	-
debian 12	ruby3.1	=3.1.2-7 \|\| =3.1.2-7+deb12u1 \|\| =3.1.2-7+hurd.1 \|\| =3.1.2-8 \|\| =3.1.2-8.1~exp1 \|\| =3.1.2-8.3 \|\| =3.1.2-8.4 \|\| =3.1.2-8.5	-
debian 13	ruby3.3	=3.3.8-2 \|\| =3.3.8-2.1 \|\| =3.3.8-2.2	-
rpm rhel10	ruby4.0	-	-

Aliases

1. CVE-2026-278202. NVD-2026-278203. OSV-DEBIAN-2026-278204. OSV-2026-278205. OSV-ALPINE-2026-278206. GHSA-g857-hhfv-j68w7. GCVE-2026-278208. SECURITY-TRACKER-CVE-2026-278209. SECURITY-CVE-2026-27820

References

1. https://github.com/ruby/zlib/security/advisories/GHSA-g857-hhfv-j68w2. https://hackerone.com/reports/34670673. https://github.com/rubysec/ruby-advisory-db/blob/master/gems/zlib/CVE-2026-27820.yml4. https://www.ruby-lang.org/en/news/2026/03/05/buffer-overflow-zlib-cve-2026-27820

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