CVE-2026-43938

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.

PUBLISHED Reserved 2026-05-04 | Published 2026-05-12 | Updated 2026-05-12 | Assigner GitHub_M

Problem types

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CWE-80: Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)

CWE-116: Improper Encoding or Escaping of Output

Product status

References

github.com/...YAFNET/security/advisories/GHSA-33gv-fc78-qgf5 exploit

github.com/...YAFNET/security/advisories/GHSA-33gv-fc78-qgf5

cve.org (CVE-2026-43938)

nvd.nist.gov (CVE-2026-43938)

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