YAFNET YetAnotherForum.NET up to 3.2.11/4.0.4 DbLogger.cs FormatStackTrace UserAgent cross site scripting

Summaryinfo

A vulnerability was found in YAFNET YetAnotherForum.NET up to 3.2.11/4.0.4. It has been rated as problematic. This affects the function FormatStackTrace of the file YAFNET.Core/Logger/DbLogger.cs. The manipulation of the argument UserAgent leads to cross site scripting. This vulnerability is documented as CVE-2026-43938. The attack can be initiated remotely. There is not any exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in YAFNET YetAnotherForum.NET up to 3.2.11/4.0.4. It has been rated as problematic. This issue affects the function FormatStackTrace of the file YAFNET.Core/Logger/DbLogger.cs. The manipulation of the argument UserAgent with an unknown input leads to a cross site scripting vulnerability. Using CWE to declare the problem leads to CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Impacted is integrity. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-43938 since 05/04/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1059.007 for this issue.

Upgrading to version 3.2.12 or 4.0.5 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Forum Software

Vendor

• YAFNET

Name

• YetAnotherForum.NET

Version

• 3.2.0
• 3.2.1
• 3.2.2
• 3.2.3
• 3.2.4
• 3.2.5
• 3.2.6
• 3.2.7
• 3.2.8
• 3.2.9
• 3.2.10
• 3.2.11
• 4.0.0
• 4.0.1
• 4.0.2
• 4.0.3
• 4.0.4

CPE 2.3info

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CPE 2.2info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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