{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-39963", "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa", "state": "PUBLISHED", "assignerShortName": "GitHub_M", "dateReserved": "2026-04-08T00:01:47.626Z", "datePublished": "2026-04-14T23:31:13.843Z", "dateUpdated": "2026-04-15T13:23:48.591Z"}, "containers": {"cna": {"title": "Serendipity: Host Header Injection enables authentication cookie scoping to an attacker-controlled domain", "problemTypes": [{"descriptions": [{"cweId": "CWE-565", "lang": "en", "description": "CWE-565: Reliance on Cookies without Validation and Integrity Checking", "type": "CWE"}]}], "metrics": [{"cvssV3_1": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 6.9, "baseSeverity": "MEDIUM", "confidentialityImpact": "HIGH", "integrityImpact": "LOW", "privilegesRequired": "NONE", "scope": "CHANGED", "userInteraction": "REQUIRED", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N", "version": "3.1"}}], "references": [{"name": "https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf", "tags": ["x_refsource_CONFIRM"], "url": "https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf"}, {"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": "2026-04-14T23:31:13.843Z"}, "descriptions": [{"lang": "en", "value": "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."}], "source": {"advisory": "GHSA-4m6c-649p-f6gf", "discovery": "UNKNOWN"}}, "adp": [{"references": [{"url": "https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf", "tags": ["exploit"]}], "metrics": [{"other": {"type": "ssvc", "content": {"timestamp": "2026-04-15T13:23:44.552367Z", "id": "CVE-2026-39963", "options": [{"Exploitation": "poc"}, {"Automatable": "no"}, {"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": "2026-04-15T13:23:48.591Z"}}]}}

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{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0,2.6.0)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "Serendipity", "source": "cna", "vendor": "s9y"}, "product": "serendipity", "vendor": "s9y"}], "analysis": {"en": {"generated_at": "2026-04-15T01:21:52.120754+00:00", "value": {"mitigation_remediation": ["Upgrade Serendipity to version 2.6.0 or later to remove the unchecked use of HTTP_HOST.", "Configure reverse proxies or load balancers to reject or sanitize Host header values so that untrusted domains cannot reach the application.", "Implement server\u2011side validation or hard\u2011code the cookie domain to prevent reliance on the HTTP_HOST header."], "summary": {"action": "Patch", "impact": "Privilege escalation via session cookie scoping"}, "threat_synthesis": {"affected_systems": "Vendors: Serendipity by s9y. Affected releases are versions 2.6\u2011beta2 and earlier. The flaw is fixed in version 2.6.0, released on GitHub. Upgrading to 2.6.0 or later eliminates the vulnerability.", "description_and_impact": "Serendipity, a PHP\u2011powered weblog engine, contains a flaw in the serendipity_setCookie() function that uses the raw HTTP_HOST header as the domain when setting cookies. Because the header is not validated, an attacker who can influence the Host header at login can force authentication cookies, including session and auto\u2011login tokens, to be scoped to an attacker\u2011controlled domain. This enables session fixation, token leakage and, for privileged users, elevation of privilege.", "risk_and_exploitability": "With a CVSS base score of 6.9, the vulnerability delivers a moderate level of risk. The documented exploit scenario requires the attacker to control the Host header, which can be achieved via TLS interception, misconfigured reverse proxies, or load\u2011balancer manipulation. No EPSS data is available, and the vulnerability is not listed in CISA's KEV catalog, but the nature of the flaw allows for remote exploitation and privilege escalation when an administrator logs in with a poisoned header. The attack vector is inferred from the description; an attacker must be able to influence HTTP requests served by the application."}}}}, "created": "2026-04-15T13:48:23.611490+00:00", "updated": "2026-04-15T14:28:41.083550+00:00", "vendors": ["s9y", "s9y$PRODUCT$serendipity"]}