YAF.NET: Stored XSS in Forum Thread Posts/Replies Allowing Arbitrary JavaScript Execution for All Thread Viewers
Priority HIGH 67CWE-116Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- Required
- Attack complexity
- Low
- Impact type
- Cross-site scripting
- Confidentiality · integrity · availability
- High · High · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-79.
Summary
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.
Why it matters now
Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00199 9th percentileScored 2026-11-07
Fix Fixed YAFNET (YAFNET): 4.0.5, 3.2.12YAFNET.Core (NuGet): 4.0.5, 3.2.12
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- No
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| YAFNET | YAFNET | 4.0.0-beta.1 to before 4.0.5; before 3.2.12 | 4.0.5, 3.2.12 | Patch available | CNA |
| — | YAFNET.Core (NuGet) | 4.0.0-beta01 to before 4.0.5 | 4.0.5 | Patch available | GHSA-8rq5-wwpp-fmj2 |
| — | YAFNET.Core (NuGet) | before 3.2.12 | 3.2.12 | Patch available | GHSA-8rq5-wwpp-fmj2 |
- YAFNET VendorYAFNET Affected 4.0.0-beta.1 to before 4.0.5; before 3.2.12 Fixed in 4.0.5, 3.2.12 Patch available CNA
- YAFNET.Core (NuGet) Vendor— Affected 4.0.0-beta01 to before 4.0.5 Fixed in 4.0.5 Patch available GHSA-8rq5-wwpp-fmj2
- YAFNET.Core (NuGet) Vendor— Affected before 3.2.12 Fixed in 3.2.12 Patch available GHSA-8rq5-wwpp-fmj2
Remediation
- Fix · CNA YAFNET (YAFNET) Fixed in 4.0.5, 3.2.12
- Fix · GHSA-8rq5-wwpp-fmj2 YAFNET.Core (NuGet) Fixed in 4.0.5 Advisory →
- Fix · GHSA-8rq5-wwpp-fmj2 YAFNET.Core (NuGet) Fixed in 3.2.12 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2026-43939
- 2026-10-03 Alias added: GHSA-8rq5-wwpp-fmj2
References
More YAFNET vulnerabilities
- TI-2026-31994 YAF.NET: Pre-Handler Authorization Bypass on Admin Pages Enabling Blind SQL Execution via `/Admin/RunSql` CVSS 3.1HIGH 8.8
- TI-2026-31995 YAF.NET: Unauthenticated Stored Second-Order XSS in Admin Event Log via Reflected `User-Agent` Header CVSS 3.1HIGH 8.1
Sources
- CVE-2026-43939 · CVE Program
- CVE-2026-43939 · NVD
- FIRST EPSS
- GHSA-8rq5-wwpp-fmj2 · GitHub Advisory Database · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences