Authenticated JavaScript execution via unsanitized thread rendering
Published May 12, 2026 · Updated May 12, 2026
Stored XSS in YAF.NET before 3.2.12 and 4.0.0-beta.1 through 4.0.4 allows remote authenticated users to run JavaScript in thread viewers' browsers. The post and reply path stores user-controlled body content, and the thread renderer returns it without adequate HTML sanitization or contextual output encoding, permitting markup to escape its surrounding context and create an event-handler element. A standard forum account with posting or reply permission is sufficient; the payload executes automatically when another user loads the thread, including a moderator or administrator, enabling same-origin actions and session compromise.
Summary
What happened
Stored XSS in YAF.NET before 3.2.12 and 4.0.0-beta.1 through 4.0.4 allows remote authenticated users to run JavaScript in thread viewers' browsers. The post and reply path stores user-controlled body content, and the thread renderer returns it without adequate HTML sanitization or contextual output encoding, permitting markup to escape its surrounding context and create an event-handler element. A standard forum account with posting or reply permission is sufficient; the payload executes automatically when another user loads the thread, including a moderator or administrator, enabling same-origin actions and session compromise.
The record
- CVE
- CVE-2026-43939
- Published
- May 12, 2026
- Updated
- May 12, 2026
- Vendor
- YetAnotherForum.NET
- Product
- YAF.NET
- Classifications
- CWE-116, CWE-80, CWE-79, T1059.007
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- May 12, 2026CVE publishedPublication date reported by the CVE source.
- May 12, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 3.2.12
- Affected versionversion=>= 4.0.0-beta.1, < 4.0.5
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Forum post and reply stored-XSS reproductionproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo