caddy — security advisory

{
  "id": "b88eba88a586a19c79a8479e304577818cd93ca288368ed1c1bf53a60c5f637e",
  "url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-27586",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "UBUNTU-CVE-2026-27586",
    "summary": "Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, two swallowed errors in `ClientAuthentication.provision()` cause mTLS client certificate authentication to silently fail open when a CA certificate file is missing, unreadable, or malformed. The server starts without error but accepts any client certificate signed by any system-trusted CA, completely bypassing the intended private CA trust boundary. Any deployment using `trusted_ca_cert_file` or `trusted_ca_certs_pem_files` for mTLS will silently degrade to accepting any system-trusted client certificate if the CA file becomes unavailable. This can happen due to a typo in the path, file rotation, corruption, or permission changes. The server gives no indication that mTLS is misconfigured. Version 2.11.1 fixes the vulnerability.",
    "evidence": "osv:UBUNTU-CVE-2026-27586",
    "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-2026-27586",
      "aliases": [
        "UBUNTU-CVE-2026-27586"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/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-2026-27586.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-2026-27586.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-2026-27586.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-2026-27586.json"
          },
          "ecosystem_specific": {
            "binaries": [
              {
                "binary_name": "caddy",
                "binary_version": "2.6.2-14ubuntu0.26.04.1~esm1"
              }
            ]
          }
        }
      ],
      "modified": "2026-10-17T12:58:49.259654897Z",
      "provider": "osv",
      "upstream": [
        "CVE-2026-27586"
      ],
      "references": [
        "https://ubuntu.com/security/CVE-2026-27586",
        "https://www.cve.org/CVERecord?id=CVE-2026-27586",
        "https://github.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7",
        "https://gist.github.com/moscowchill/9566c79c76c0b64c57f8bd0716f97c48",
        "https://github.com/caddyserver/caddy/releases/tag/v2.11.1"
      ]
    },
    "related_cves": [
      {
        "value": "CVE-2026-27586",
        "evidence": "/upstream"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/1/score"
  },
  "source_id": "core-osv",
  "document_id": 359089,
  "published_at": "2026-02-24T17:29:00+00:00"
}