{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "cpe": "cpe:2.3:a:s9y:serendipity:*:*:*:*:*:*:*:*",
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "2.6.0"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "CPE_RANGE",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "87696c92730d75785d17b515125be3862cdfb49e"
            }
          ],
          "repo": "https://github.com/s9y/serendipity",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-458g-q4fh-mj6r"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-113"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/39xxx/CVE-2026-39971.json"
  },
  "details": "Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the email sending functionality in include/functions.inc.php inserts $_SERVER['HTTP_HOST'] directly into the Message-ID SMTP header without validation, and the existing sanitization function serendipity_isResponseClean() is not called on HTTP_HOST before embedding it. An attacker who can control the Host header during an email-triggering action such as comment notifications or subscription emails can inject arbitrary SMTP headers into outgoing emails. This enables identity spoofing, reply hijacking via manipulated Message-ID threading, and email reputation abuse through the attacker's domain being embedded in legitimate mail headers. This issue has been fixed in version 2.6.0.",
  "id": "CVE-2026-39971",
  "modified": "2026-08-12T03:51:45.383078601Z",
  "published": "2026-04-14T23:35:49.305Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/s9y/Serendipity/releases/tag/2.6.0"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/39xxx/CVE-2026-39971.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-39971"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Serendipity: Host Header Injection leads to SMTP header injection via unvalidated HTTP_HOST"
}