CVE-2026-43938: Yafnet

High severity, CVSS 8.1. EPSS: 0.4% chance of exploitation in the next 30 days.

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 products

• Yafnet Yafnet: from 4.0.0-beta.1, before 4.0.5 (fixed in 4.0.5); before 3.2.12 (fixed in 3.2.12)

Published 2026-05-12. Last modified 2026-06-17.