{"id":"CVE-2026-43938","aliases":["GHSA-33gv-fc78-qgf5"],"url":"https://o3.security/vulnerability/CVE-2026-43938","summary":"YAF.NET: Unauthenticated Stored Second-Order XSS in Admin Event Log via Reflected `User-Agent` Header","details":"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.","published":"2026-05-12T13:57:56.951Z","modified":"2026-08-07T11:31:22.670732716Z","cvss":{"score":8.1,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"NuGet","name":"YAFNET.Core","fixedVersion":"4.0.5"},{"ecosystem":"NuGet","name":"YAFNET.Core","fixedVersion":"3.2.12"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43938.json"},{"type":"ADVISORY","url":"https://github.com/YAFNET/YAFNET/security/advisories/GHSA-33gv-fc78-qgf5"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-43938"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T11:31:22.670732716Z"}}