{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-39971","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","state":"PUBLISHED","assignerShortName":"GitHub_M","dateReserved":"2026-04-08T00:01:47.627Z","datePublished":"2026-04-14T23:35:49.305Z","dateUpdated":"2026-04-15T16:22:04.004Z"},"containers":{"cna":{"title":"Serendipity: Host Header Injection leads to SMTP header injection via unvalidated HTTP_HOST","problemTypes":[{"descriptions":[{"cweId":"CWE-113","lang":"en","description":"CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')","type":"CWE"}]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":7.2,"baseSeverity":"HIGH","confidentialityImpact":"LOW","integrityImpact":"LOW","privilegesRequired":"NONE","scope":"CHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N","version":"3.1"}}],"references":[{"name":"https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r","tags":["x_refsource_CONFIRM"],"url":"https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r"},{"name":"https://github.com/s9y/Serendipity/releases/tag/2.6.0","tags":["x_refsource_MISC"],"url":"https://github.com/s9y/Serendipity/releases/tag/2.6.0"}],"affected":[{"vendor":"s9y","product":"Serendipity","versions":[{"version":"< 2.6.0","status":"affected"}]}],"providerMetadata":{"orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","shortName":"GitHub_M","dateUpdated":"2026-04-14T23:35:49.305Z"},"descriptions":[{"lang":"en","value":"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."}],"source":{"advisory":"GHSA-458g-q4fh-mj6r","discovery":"UNKNOWN"}},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-04-15T16:20:55.327550Z","id":"CVE-2026-39971","options":[{"Exploitation":"poc"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-04-15T16:22:04.004Z"}}]}}