What’s Vulnerable › Vulnerabilities

CVE-2026-43939: YAF.NET: Stored XSS in Forum Thread Posts/Replies Allowing Arbitrary JavaScript Execution for All Thread Viewers

• Severity: high (CVSS 7.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-12 · updated 2026-06-17
• Weakness: CWE-79

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.

Affected products

• YAFNET: from 4.0.0-beta.1, < 4.0.5; before 3.2.12

References

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

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