CVE-2026-43939 PUBLISHED

YAF.NET: Stored XSS in Forum Thread Posts/Replies Allowing Arbitrary JavaScript Execution for All Thread Viewers

Assigner: GitHub_M
Reserved: 04.05.2026 Published: 12.05.2026 Updated: 12.05.2026

YetAnotherForum.NET (YAF.NET) is a C# ASP.NET forum. Prior to 4.0.5 and 3.2.12, the thread posting and reply feature accepts user-supplied content via a a post or reply that is stored server-side and later rendered back into the thread page without adequate HTML sanitization or contextual output encoding. This vulnerability is fixed in 4.0.5 and 3.2.12.

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N
CVSS Score: 7.3

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	High
Privileges Required	Low	Integrity Impact	High
User Interaction	Required	Availability Impact	None

CVSS 3.1

Product Status

Vendor	YAFNET
Product	YAFNET
Versions	Version >= 4.0.0-beta.1, < 4.0.5 is affected Version < 3.2.12 is affected

References

https://github.com/YAFNET/YAFNET/security/advisories/GHSA-8rq5-wwpp-fmj2

Problem Types

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') CWE
CWE-80: Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS) CWE
CWE-116: Improper Encoding or Escaping of Output CWE