CVE-2026-43938
HighSummary
In YetAnotherForum.NET prior to versions 4.0.5 and 3.2.12, there is a vulnerability related to improper handling of the User-Agent header. The application logs this header in the event log and then interpolates it directly into HTML without proper encoding, which may lead to XSS attacks.
Risk Assessment
Organizations using the vulnerable version may be exposed to XSS attacks, potentially leading to session hijacking or injection of malicious code.
Recommendation
It is recommended to upgrade to version 4.0.5 or 3.2.12 to mitigate this vulnerability. Additionally, implementing proper input encoding mechanisms in the application is advisable.
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Original NVD description (English source)
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.