{"id":"CVE-2026-43938","state":"PUBLISHED","title":"YAF.NET: Unauthenticated Stored Second-Order XSS in Admin Event Log via Reflected `User-Agent` Header","description":"YetAnotherForum.NET (YAF.NET) is a C# ASP.NET forum. Prior to 4.0.5 and 3.2.12, the application's database logger (YAFNET.Core/Logger/DbLogger.cs) captures the incoming request's User-Agent header into a JObject, serializes it with JsonConvert, and stores the result in the EventLog.Description column whenever an event (e.g., an unhandled exception) is logged. The admin event-log page (YetAnotherForum.NET/Pages/Admin/EventLog.cshtml.cs) later deserializes that JSON in FormatStackTrace() and interpolates the UserAgent value directly into an HTML string with no encoding, and the Razor view EventLog.cshtml emits the result through @Html.Raw. This vulnerability is fixed in 4.0.5 and 3.2.12.","publishedAt":"2026-05-12T13:57:56.951Z","updatedAt":"2026-05-12T15:39:46.446Z","severity":{"score":8.1,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["YAFNET YAFNET"],"affected":[{"vendor":"YAFNET","product":"YAFNET","versions":[{"version":">= 4.0.0-beta.1, < 4.0.5","status":"affected"},{"version":"< 3.2.12","status":"affected"}]}],"references":["https://github.com/YAFNET/YAFNET/security/advisories/GHSA-33gv-fc78-qgf5"],"weaknesses":["CWE-79","CWE-80","CWE-116"],"ingestedAt":"2026-10-29T20:11:57.932Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/43xxx/CVE-2026-43938.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-43938","state":"PUBLISHED","datePublished":"2026-05-12T13:57:56.951Z","dateUpdated":"2026-05-12T15:39:46.446Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-05-04T16:59:09.089Z"},"containers":{"cna":{"title":"YAF.NET: Unauthenticated Stored Second-Order XSS in Admin Event Log via Reflected `User-Agent` Header","descriptions":[{"lang":"en","value":"YetAnotherForum.NET (YAF.NET) is a C# ASP.NET forum. Prior to 4.0.5 and 3.2.12, the application's database logger (YAFNET.Core/Logger/DbLogger.cs) captures the incoming request's User-Agent header into a JObject, serializes it with JsonConvert, and stores the result in the EventLog.Description column whenever an event (e.g., an unhandled exception) is logged. The admin event-log page (YetAnotherForum.NET/Pages/Admin/EventLog.cshtml.cs) later deserializes that JSON in FormatStackTrace() and interpolates the UserAgent value directly into an HTML string with no encoding, and the Razor view EventLog.cshtml emits the result through @Html.Raw. This vulnerability is fixed in 4.0.5 and 3.2.12."}],"affected":[{"vendor":"YAFNET","product":"YAFNET","versions":[{"version":">= 4.0.0-beta.1, < 4.0.5","status":"affected"},{"version":"< 3.2.12","status":"affected"}]}],"references":[{"url":"https://github.com/YAFNET/YAFNET/security/advisories/GHSA-33gv-fc78-qgf5","name":"https://github.com/YAFNET/YAFNET/security/advisories/GHSA-33gv-fc78-qgf5","tags":["x_refsource_CONFIRM"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":8.1,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"REQUIRED","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-79","lang":"en","description":"CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-80","lang":"en","description":"CWE-80: Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-116","lang":"en","description":"CWE-116: Improper Encoding or Escaping of Output","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-05-12T13:57:56.951Z"},"source":{"advisory":"GHSA-33gv-fc78-qgf5","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/YAFNET/YAFNET/security/advisories/GHSA-33gv-fc78-qgf5","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-05-12T15:39:17.598324Z","id":"CVE-2026-43938","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-05-12T15:39:46.446Z"}}]}}}