{"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": "2026-04-14T23:35:49.305Z"}, "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"}}}}

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