{"id":"CVE-2026-39963","aliases":["EUVD-2026-22809","GHSA-4m6c-649p-f6gf"],"status":"published","title":"Serendipity: Host Header Injection enables authentication cookie scoping to an attacker-controlled domain","description":"Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2  and below, the serendipity_setCookie() function in include/functions_config.inc.php uses $_SERVER['HTTP_HOST'] without validation as the domain parameter of setcookie(). An attacker who can influence the Host header at login time, such as via MITM, reverse proxy misconfiguration, or load balancer manipulation, can force authentication cookies including session tokens and auto-login tokens to be scoped to an attacker-controlled domain. This enables session fixation, token leakage to attacker-controlled infrastructure, and privilege escalation if an admin logs in under a poisoned Host header. This issue has been fixed in version 2.6.0.","severity":{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.00224,"percentile":0.13125,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-565"],"published":"2026-04-14T22:32:29Z","modified":"2026-10-28T02:30:26Z","fixes":[{"ecosystem":"Packagist","package":"s9y/serendipity","fixed_in":["2.6.0"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"Packagist","package":"s9y/serendipity","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.6.0"}]}]},{"source":"osv","ecosystem":"Packagist","package":"s9y/serendipity","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.6.0"}]}],"versions":["2.0.0","2.0.1","2.0.2","2.0.3","2.0.4","2.0.5","2.1-beta1","2.1-beta2","2.1-beta3","2.1-rc1","2.1.0","2.1.1","2.1.2","2.1.3","2.1.4","2.1.5","2.1.6","2.2.1-alpha1","2.3-beta1","2.3-rc1","2.3.0","2.3.1","2.3.2","2.3.3","2.3.4","2.3.5","2.4-beta1","2.4.0","2.5-beta1","2.5.0","2.6-beta1"]}],"products":[{"vendor":"s9y","product":"serendipity"}],"references":[{"url":"https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf","tags":["x_refsource_CONFIRM","exploit","Exploit","Mitigation","Vendor Advisory","advisory","web"]},{"url":"https://github.com/s9y/Serendipity/releases/tag/2.6.0","tags":["x_refsource_MISC","Product","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-39963","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-4m6c-649p-f6gf"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/39xxx/CVE-2026-39963.json","tags":["advisory"]},{"url":"https://github.com/s9y/Serendipity","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-39963","title":"Serendipity: Host Header Injection enables authentication cookie scoping to an attacker-controlled domain","description":"Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2  and below, the serendipity_setCookie() function in include/functions_config.inc.php uses $_SERVER['HTTP_HOST'] without validation as the domain parameter of setcookie(). An attacker who can influence the Host header at login time, such as via MITM, reverse proxy misconfiguration, or load balancer manipulation, can force authentication cookies including session tokens and auto-login tokens to be scoped to an attacker-controlled domain. This enables session fixation, token leakage to attacker-controlled infrastructure, and privilege escalation if an admin logs in under a poisoned Host header. This issue has been fixed in version 2.6.0.","status":"published","published":"2026-04-14T23:31:13.843Z","modified":"2026-04-15T13:23:48.591Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-565"],"updated_at":"2026-11-02T14:20:02.662847Z"}],"euvd":[{"id":"EUVD-2026-22809","description":"Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2  and below, the serendipity_setCookie() function in include/functions_config.inc.php uses $_SERVER['HTTP_HOST'] without validation as the domain parameter of setcookie(). An attacker who can influence the Host header at login time, such as via MITM, reverse proxy misconfiguration, or load balancer manipulation, can force authentication cookies including session tokens and auto-login tokens to be scoped to an attacker-controlled domain. This enables session fixation, token leakage to attacker-controlled infrastructure, and privilege escalation if an admin logs in under a poisoned Host header. This issue has been fixed in version 2.6.0.","status":"published","published":"2026-04-14T23:31:13Z","modified":"2026-04-15T13:23:48Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T19:24:25.607055Z"}],"ghsa":[{"id":"GHSA-4m6c-649p-f6gf","title":"Serendipity has a Host Header Injection allows authentication cookie scoping to attacker-controlled domain in functions_config.inc.php","description":"### Summary\nThe `serendipity_setCookie()` function uses `$_SERVER['HTTP_HOST']` without validation as the `domain` parameter of `setcookie()`. An attacker can force authentication cookies — including session tokens and auto-login tokens — to be scoped to an attacker-controlled domain, facilitating session hijacking.\n\n### Details\nIn `include/functions_config.inc.php:726`:\n```php\nfunction serendipity_setCookie($name, $value, $securebyprot = true, ...) {\n    $host = $_SERVER['HTTP_HOST']; // ← attacker-controlled, no validation\n\n    if ($securebyprot) {\n        if ($pos = strpos($host, \":\")) {\n            $host = substr($host, 0, $pos); // strips port only\n        }\n    }\n\n    setcookie(\"serendipity[$name]\", $value, [\n        'domain'   =\u003e $host,   // ← poisoned domain\n        'httponly' =\u003e $httpOnly,\n        'samesite' =\u003e 'Strict'\n    ]);\n}\n```\n\nThis function is called during login with sensitive cookies:\n```php\n// functions_config.inc.php:455-498\nserendipity_setCookie('author_autologintoken', $rnd, true, false, true);\nserendipity_setCookie('author_username', $user);\nserendipity_setCookie('author_token', $hash);\n```\n\nIf an attacker can influence the `Host` header at login time (e.g. via MITM, reverse proxy misconfiguration, or load balancer), authentication cookies are issued scoped to the attacker's domain instead of the legitimate one.\n\n### PoC\n```bash\ncurl -v -X POST \\\n  -H \"Host: attacker.com\" \\\n  -d \"serendipity[user]=admin\u0026serendipity[pass]=admin\" \\\n  http://[TARGET]/serendipity_admin.php 2\u003e\u00261 | grep -i \"set-cookie\"\n```\n\nExpected output:\n```http\nSet-Cookie: serendipity[author_token]=; domain=attacker.com; HttpOnly\n```\n\n### Impact\n- **Session fixation** — attacker pre-sets a cookie scoped to their domain, then tricks the victim into authenticating, inheriting the poisoned token\n- **Token leakage** — `author_autologintoken` scoped to wrong domain may be sent to attacker-controlled infrastructure\n- **Privilege escalation** — if admin logs in under a poisoned Host header, their admin token is compromised\n\n### Suggested Fix\nValidate `HTTP_HOST` against the configured `$serendipity['url']` before use:\n```php\nfunction serendipity_setCookie($name, $value, ...) {\n    global $serendipity;\n    $configured = parse_url($serendipity['url'], PHP_URL_HOST);\n    $host = preg_replace('/:[0-9]+$/', '', $_SERVER['HTTP_HOST']);\n    $host = ($host === $configured) ? $host : $configured;\n\n    setcookie(\"serendipity[$name]\", $value, [\n        'domain' =\u003e $host,\n        ...\n    ]);\n}\n```","status":"published","published":"2026-04-14T22:32:29Z","modified":"2026-04-15T21:14:20Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium"}],"cwes":["CWE-565"],"updated_at":"2026-11-02T14:39:54.128054Z"}],"nvd":[{"id":"CVE-2026-39963","description":"Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2  and below, the serendipity_setCookie() function in include/functions_config.inc.php uses $_SERVER['HTTP_HOST'] without validation as the domain parameter of setcookie(). An attacker who can influence the Host header at login time, such as via MITM, reverse proxy misconfiguration, or load balancer manipulation, can force authentication cookies including session tokens and auto-login tokens to be scoped to an attacker-controlled domain. This enables session fixation, token leakage to attacker-controlled infrastructure, and privilege escalation if an admin logs in under a poisoned Host header. This issue has been fixed in version 2.6.0.","status":"published","published":"2026-04-15T04:17:39.58Z","modified":"2026-10-26T22:10:00.163Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium","assessor":"secondary"}],"cwes":["CWE-565"],"updated_at":"2026-11-02T14:12:14.748836Z"}],"osv":[{"id":"CVE-2026-39963","title":"Serendipity: Host Header Injection enables authentication cookie scoping to an attacker-controlled domain","description":"Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2  and below, the serendipity_setCookie() function in include/functions_config.inc.php uses $_SERVER['HTTP_HOST'] without validation as the domain parameter of setcookie(). An attacker who can influence the Host header at login time, such as via MITM, reverse proxy misconfiguration, or load balancer manipulation, can force authentication cookies including session tokens and auto-login tokens to be scoped to an attacker-controlled domain. This enables session fixation, token leakage to attacker-controlled infrastructure, and privilege escalation if an admin logs in under a poisoned Host header. This issue has been fixed in version 2.6.0.","status":"published","published":"2026-04-14T23:31:13.843Z","modified":"2026-10-28T02:30:26.284446799Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium"}],"cwes":["CWE-565"],"updated_at":"2026-11-02T15:45:03.040464Z"},{"id":"GHSA-4m6c-649p-f6gf","title":"Serendipity has a Host Header Injection allows authentication cookie scoping to attacker-controlled domain in functions_config.inc.php","description":"### Summary\nThe `serendipity_setCookie()` function uses `$_SERVER['HTTP_HOST']` without validation as the `domain` parameter of `setcookie()`. An attacker can force authentication cookies — including session tokens and auto-login tokens — to be scoped to an attacker-controlled domain, facilitating session hijacking.\n\n### Details\nIn `include/functions_config.inc.php:726`:\n```php\nfunction serendipity_setCookie($name, $value, $securebyprot = true, ...) {\n    $host = $_SERVER['HTTP_HOST']; // ← attacker-controlled, no validation\n\n    if ($securebyprot) {\n        if ($pos = strpos($host, \":\")) {\n            $host = substr($host, 0, $pos); // strips port only\n        }\n    }\n\n    setcookie(\"serendipity[$name]\", $value, [\n        'domain'   =\u003e $host,   // ← poisoned domain\n        'httponly' =\u003e $httpOnly,\n        'samesite' =\u003e 'Strict'\n    ]);\n}\n```\n\nThis function is called during login with sensitive cookies:\n```php\n// functions_config.inc.php:455-498\nserendipity_setCookie('author_autologintoken', $rnd, true, false, true);\nserendipity_setCookie('author_username', $user);\nserendipity_setCookie('author_token', $hash);\n```\n\nIf an attacker can influence the `Host` header at login time (e.g. via MITM, reverse proxy misconfiguration, or load balancer), authentication cookies are issued scoped to the attacker's domain instead of the legitimate one.\n\n### PoC\n```bash\ncurl -v -X POST \\\n  -H \"Host: attacker.com\" \\\n  -d \"serendipity[user]=admin\u0026serendipity[pass]=admin\" \\\n  http://[TARGET]/serendipity_admin.php 2\u003e\u00261 | grep -i \"set-cookie\"\n```\n\nExpected output:\n```http\nSet-Cookie: serendipity[author_token]=; domain=attacker.com; HttpOnly\n```\n\n### Impact\n- **Session fixation** — attacker pre-sets a cookie scoped to their domain, then tricks the victim into authenticating, inheriting the poisoned token\n- **Token leakage** — `author_autologintoken` scoped to wrong domain may be sent to attacker-controlled infrastructure\n- **Privilege escalation** — if admin logs in under a poisoned Host header, their admin token is compromised\n\n### Suggested Fix\nValidate `HTTP_HOST` against the configured `$serendipity['url']` before use:\n```php\nfunction serendipity_setCookie($name, $value, ...) {\n    global $serendipity;\n    $configured = parse_url($serendipity['url'], PHP_URL_HOST);\n    $host = preg_replace('/:[0-9]+$/', '', $_SERVER['HTTP_HOST']);\n    $host = ($host === $configured) ? $host : $configured;\n\n    setcookie(\"serendipity[$name]\", $value, [\n        'domain' =\u003e $host,\n        ...\n    ]);\n}\n```","status":"published","published":"2026-04-14T22:32:29Z","modified":"2026-04-15T21:35:53.81683Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium"}],"cwes":["CWE-565"],"updated_at":"2026-11-02T15:46:37.148947Z"}]}}