CVE-2026-43938
YAFNET has Unauthenticated Stored Second-Order XSS in Admin Event Log via Reflected `User-Agent` Header
Impact
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 packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| nuget | YAFNET.Core | >= 4.0.0-beta01, <= 4.0.4 | 4.0.5 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-33gv-fc78-qgf5
- https://github.com/YAFNET/YAFNET/security/advisories/GHSA-33gv-fc78-qgf5
- https://github.com/YAFNET/YAFNET/releases/tag/v3.2.12
- https://github.com/YAFNET/YAFNET/releases/tag/v4.0.5
- https://nvd.nist.gov/vuln/detail/CVE-2026-43938