CVE-2026-43939

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

State: Published
Severity: 7.3 High
Published: May 12, 2026
Updated: May 13, 2026
Reserved: May 4, 2026

Description

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.

Scores

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

Weaknesses

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

Affected Products

Product	Versions
YAFNETYAFNET	>= 4.0.0-beta.1, < 4.0.5Affected < 3.2.12Affected

References

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

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