CVE-2026-43938 Details
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.
A stored cross-site scripting vulnerability has been identified in YetAnotherForum.NET (YAF.NET) versions prior to 4.0.5 and 3.2.12. The issue arises in the application's database logger, which captures the User-Agent header from incoming requests, serializes it as JSON, and stores it in the EventLog.Description column. This data is later deserialized and rendered as HTML in the admin event-log page, without proper sanitization. The vulnerability can be exploited by sending a single HTTP request with a malicious User-Agent header to a public, unauthenticated endpoint, which then persists the payload. When an administrator views the event log, the injected script executes in their browser, potentially leading to a full forum takeover.
Users can upgrade to YetAnotherForum.NET versions 4.0.5 or 3.2.12 to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed May 12, 2026CISA-ADP
Assessed May 12, 2026References to Advisories, Solutions, and Tools
By selecting these links, you will be leaving this site. These are references gathered from the official CVE record and are not endorsed by Volerion.
| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/YAFNET/YAFNET/security/advisories/GHSA-33gv-fc78-qgf5 | CISA-ADP | AdvisoryExploitRemedyVendor |
| https://github.com/YAFNET/YAFNET/security/advisories/GHSA-33gv-fc78-qgf5 | [email protected] | AdvisoryExploitRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-116 | Improper Encoding or Escaping of Output | [email protected] |
| CWE-79 | Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') | [email protected] |
| CWE-80 | Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS) | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| YetAnotherForum.NET | 4.0.4 (semver) <= 3.2.11 (semver) |
CPE
Remediation
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Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| May 12, 2026 | CVE Modified | CISA-ADP |
| May 12, 2026 | New CVE Received | [email protected] |