ruby3.1, ruby3.3 — security advisory
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.
- Products
- ruby3.1, ruby3.3
- Affected versions
- 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, 3.3.8-2, 3.3.8-2.1, 3.3.8-2.2
- Fixed versions
- Not specified
- CVEs
- CVE-2026-27820
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 1 Nov 2026, 17:47 UTC · Revision 2
Source evidence
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.
osv:DEBIAN-CVE-2026-27820
ruby3.1
Fixed versions: Not specified
ruby3.3
Fixed versions: Not specified
ruby3.3
Fixed versions: Not specified
Complete source record
{
"id": "f91e5f6da049155c1a20b48b92272ffb09e64d661f1b3b568c9d2ae66740cb5c",
"url": "https://osv.dev/vulnerability/DEBIAN-CVE-2026-27820",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "DEBIAN-CVE-2026-27820",
"summary": "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.",
"evidence": "osv:DEBIAN-CVE-2026-27820",
"products": [
{
"name": {
"value": "ruby3.1",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.1.2-7",
"evidence": "/affected/0/versions"
},
{
"value": "3.1.2-7+deb12u1",
"evidence": "/affected/0/versions"
},
{
"value": "3.1.2-7+hurd.1",
"evidence": "/affected/0/versions"
},
{
"value": "3.1.2-8",
"evidence": "/affected/0/versions"
},
{
"value": "3.1.2-8.1~exp1",
"evidence": "/affected/0/versions"
},
{
"value": "3.1.2-8.3",
"evidence": "/affected/0/versions"
},
{
"value": "3.1.2-8.4",
"evidence": "/affected/0/versions"
},
{
"value": "3.1.2-8.5",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "ruby3.3",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.3.8-2",
"evidence": "/affected/1/versions"
},
{
"value": "3.3.8-2.1",
"evidence": "/affected/1/versions"
},
{
"value": "3.3.8-2.2",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
"value": "ruby3.3",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.3.8-2",
"evidence": "/affected/2/versions"
},
{
"value": "3.3.8-2.1",
"evidence": "/affected/2/versions"
},
{
"value": "3.3.8-2.2",
"evidence": "/affected/2/versions"
}
]
}
],
"severity": "critical",
"structured": {
"id": "DEBIAN-CVE-2026-27820",
"aliases": [
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],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
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"introduced": "0"
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],
"package": {
"name": "ruby3.1",
"purl": "pkg:deb/debian/ruby3.1?arch=source&distro=bookworm",
"ecosystem": "Debian:12"
},
"versions": [
"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"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-27820.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "ruby3.3",
"purl": "pkg:deb/debian/ruby3.3?arch=source&distro=trixie",
"ecosystem": "Debian:13"
},
"versions": [
"3.3.8-2",
"3.3.8-2.1",
"3.3.8-2.2"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-27820.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
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],
"package": {
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"purl": "pkg:deb/debian/ruby3.3?arch=source&distro=forky",
"ecosystem": "Debian:14"
},
"versions": [
"3.3.8-2",
"3.3.8-2.1",
"3.3.8-2.2"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-27820.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
}
],
"modified": "2026-10-27T09:47:36.219374804Z",
"provider": "osv",
"upstream": [
"CVE-2026-27820"
],
"references": [
"https://security-tracker.debian.org/tracker/CVE-2026-27820"
]
},
"related_cves": [
{
"value": "CVE-2026-27820",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 461189,
"published_at": "2026-04-16T18:16:44.77+00:00"
}