Critical
caddy — security advisory
Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's HTTP `host` request matcher is documented as case-insensitive, but when configured with a large host list (>100 entries) it becomes case-sensitive due to an optimized matching path. An attacker can bypass host-based routing and any access controls attached to that route by changing the casing of the `Host` header. Version 2.11.1 contains a fix for the issue.
- Products
- caddy
- Affected versions
- 2.11.4-1, 2.6.2-11, 2.6.2-12, 2.6.2-14, 2.6.2-14ubuntu0.26.04.1~esm1, 2.6.2-6, 2.6.2-6ubuntu0.24.04.1, 2.6.2-6ubuntu0.24.04.2, 2.6.2-6ubuntu0.24.04.2+esm1, 2.6.2-6ubuntu0.24.04.3, 2.6.2-6ubuntu0.24.04.3+esm1, 2.6.2-6ubuntu0.24.04.3+esm2, 2.6.2-9
- Fixed versions
- Not specified
- CVEs
- CVE-2026-27588
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 02:42 UTC · Revision 1
Source evidence
Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's HTTP `host` request matcher is documented as case-insensitive, but when configured with a large host list (>100 entries) it becomes case-sensitive due to an optimized matching path. An attacker can bypass host-based routing and any access controls attached to that route by changing the casing of the `Host` header. Version 2.11.1 contains a fix for the issue.
osv:UBUNTU-CVE-2026-27588
caddy
Fixed versions: Not specified
caddy
Fixed versions: Not specified
caddy
Fixed versions: Not specified
caddy
Fixed versions: Not specified
Complete source record
{
"id": "1197e1c6128f74ef89b870364af07807db400d2806e1ab6c6f31d9f796ae6a0d",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-27588",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-27588",
"summary": "Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's HTTP `host` request matcher is documented as case-insensitive, but when configured with a large host list (>100 entries) it becomes case-sensitive due to an optimized matching path. An attacker can bypass host-based routing and any access controls attached to that route by changing the casing of the `Host` header. Version 2.11.1 contains a fix for the issue.",
"evidence": "osv:UBUNTU-CVE-2026-27588",
"products": [
{
"name": {
"value": "caddy",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "2.6.2-6",
"evidence": "/affected/0/versions"
},
{
"value": "2.6.2-6ubuntu0.24.04.1",
"evidence": "/affected/0/versions"
},
{
"value": "2.6.2-6ubuntu0.24.04.2",
"evidence": "/affected/0/versions"
},
{
"value": "2.6.2-6ubuntu0.24.04.2+esm1",
"evidence": "/affected/0/versions"
},
{
"value": "2.6.2-6ubuntu0.24.04.3",
"evidence": "/affected/0/versions"
},
{
"value": "2.6.2-6ubuntu0.24.04.3+esm1",
"evidence": "/affected/0/versions"
},
{
"value": "2.6.2-6ubuntu0.24.04.3+esm2",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "caddy",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "2.6.2-9",
"evidence": "/affected/1/versions"
},
{
"value": "2.6.2-11",
"evidence": "/affected/1/versions"
},
{
"value": "2.6.2-12",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
"value": "caddy",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "2.6.2-14",
"evidence": "/affected/2/versions"
},
{
"value": "2.11.4-1",
"evidence": "/affected/2/versions"
}
]
},
{
"name": {
"value": "caddy",
"evidence": "/affected/3/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "2.6.2-12",
"evidence": "/affected/3/versions"
},
{
"value": "2.6.2-14",
"evidence": "/affected/3/versions"
},
{
"value": "2.6.2-14ubuntu0.26.04.1~esm1",
"evidence": "/affected/3/versions"
}
]
}
],
"severity": "critical",
"structured": {
"id": "UBUNTU-CVE-2026-27588",
"aliases": [
"UBUNTU-CVE-2026-27588"
],
"metrics": [
{
"type": "CVSS_V4",
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P"
},
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N"
},
{
"type": "Ubuntu",
"score": "medium"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "caddy",
"purl": "pkg:deb/ubuntu/caddy?arch=source&distro=esm-apps%2Fnoble",
"ecosystem": "Ubuntu:Pro:24.04:LTS"
},
"versions": [
"2.6.2-6",
"2.6.2-6ubuntu0.24.04.1",
"2.6.2-6ubuntu0.24.04.2",
"2.6.2-6ubuntu0.24.04.2+esm1",
"2.6.2-6ubuntu0.24.04.3",
"2.6.2-6ubuntu0.24.04.3+esm1",
"2.6.2-6ubuntu0.24.04.3+esm2"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-27588.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "caddy",
"binary_version": "2.6.2-6ubuntu0.24.04.3+esm2"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "caddy",
"purl": "pkg:deb/ubuntu/caddy?arch=source&distro=questing",
"ecosystem": "Ubuntu:25.10"
},
"versions": [
"2.6.2-9",
"2.6.2-11",
"2.6.2-12"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-27588.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "caddy",
"binary_version": "2.6.2-12"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "caddy",
"purl": "pkg:deb/ubuntu/caddy?arch=source&distro=stonking",
"ecosystem": "Ubuntu:26.10"
},
"versions": [
"2.6.2-14",
"2.11.4-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-27588.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "caddy",
"binary_version": "2.11.4-1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "caddy",
"purl": "pkg:deb/ubuntu/caddy?arch=source&distro=esm-apps%2Fresolute",
"ecosystem": "Ubuntu:Pro:26.04:LTS"
},
"versions": [
"2.6.2-12",
"2.6.2-14",
"2.6.2-14ubuntu0.26.04.1~esm1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-27588.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "caddy",
"binary_version": "2.6.2-14ubuntu0.26.04.1~esm1"
}
]
}
}
],
"modified": "2026-10-17T12:58:48.933278964Z",
"provider": "osv",
"upstream": [
"CVE-2026-27588"
],
"references": [
"https://ubuntu.com/security/CVE-2026-27588",
"https://www.cve.org/CVERecord?id=CVE-2026-27588",
"https://github.com/caddyserver/caddy/security/advisories/GHSA-x76f-jf84-rqj8",
"https://github.com/caddyserver/caddy/releases/tag/v2.11.1"
]
},
"related_cves": [
{
"value": "CVE-2026-27588",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/1/score"
},
"source_id": "core-osv",
"document_id": 359079,
"published_at": "2026-02-24T17:29:00+00:00"
}