Cyber Resilience

CVE-2026-43939

High

Published: 12 May 2026

Published
12 May 2026
Modified
13 May 2026
KEV Added
—
Patch
—
CVSS Score v3.1 7.3 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N
EPSS Score 0.0003 10.1th percentile
Risk Priority 15 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-43939 is a high-severity Cross-site Scripting (CWE-79) vulnerability. Its CVSS base score is 7.3 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 10.1th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

EU & UK References

Vulnerability details

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…

more

adequate HTML sanitization or contextual output encoding. This vulnerability is fixed in 4.0.5 and 3.2.12.

CWE(s)
CWE-79CWE-80CWE-116

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
Why these techniques?

Stored XSS in public-facing forum app directly enables exploitation of the web application via unsanitized user content.

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

CVEs Like This One

CVE-2026-43938Shared CWE-116, CWE-79
CVE-2025-21612Shared CWE-79, CWE-80
CVE-2021-47873Shared CWE-79
CVE-2026-7052Shared CWE-79
CVE-2024-56060Shared CWE-79
CVE-2025-49043Shared CWE-79
CVE-2026-40038Shared CWE-79
CVE-2024-56022Shared CWE-79
CVE-2025-68889Shared CWE-79
CVE-2026-1074Shared CWE-79

Affected Assets

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

SI-15 Information Output Filtering
addresses: CWE-79 CWE-116

Output validation against expected content can reject or sanitize script content in generated web pages, reducing XSS exploitability.

CA-8 Penetration Testing
addresses: CWE-79

Penetration testing submits XSS payloads to web applications, detecting cross-site scripting flaws for subsequent remediation.

SI-10 Information Input Validation
addresses: CWE-79

Validates web inputs to reject script-related content that could produce XSS.

References