dbcve.org
Cross-site Scripting (XSS)Weakness · CWE-79

CVE-2026-43939

HIGH · 7.3 CVSS v3.1 Published 2026-05-12
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
77/100
Remediation priority · High
Remotely reachable

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

YetAnotherForum.NET versions prior to 4.0.5 and 3.2.12 contain a stored cross-site scripting (XSS) vulnerability in the thread posting and reply feature. User-supplied content in posts and replies is stored server-side and rendered back into thread pages without adequate HTML sanitization or contextual output encoding, allowing attackers to inject malicious scripts that execute in other users' browsers.

MitigationUpgrade to YAF.NET version 4.0.5 or 3.2.12 or later, which implements proper HTML sanitization and contextual output encoding for user-submitted content in posts and replies.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify YAF installation location
    Locate the YetAnotherForum.NET installation by checking web application directories, commonly found in IIS web roots or the application's bin folder for YAF.dll or YetAnotherForum.NET assemblies
    Affected if YAF.NET software is present on the system
  2. Determine installed YAF version
    Check the assembly version of YAF.dll in the bin directory, or view the version displayed in the forum footer/admin panel under 'Version Information'
    Affected if Version cannot be determined or is lower than 4.0.5 (for 4.x branch) or lower than 3.2.12 (for 3.x branch)
  3. Confirm forum posting feature is accessible
    Verify that the forum allows registered users to create new threads and post replies - check if the posting/reply functionality is enabled in admin settings
    Affected if Posting and reply features are enabled and users can submit content
  4. Verify XSS protection status
    Inspect the HTML output of a test post/reply using browser developer tools or view source to check if user-submitted content is being rendered with proper encoding or sanitization
    Affected if Raw HTML or unencoded script tags appear in rendered post content

A user is affected if their YAF.NET installation runs version 4.0.5之前的版本或3.2.12之前的版本 and the posting/reply feature is enabled, allowing unsanitized user content to be stored and rendered to other users.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to YAF.NET version 4.0.5 or 3.2.12 or later, which implements proper HTML sanitization and contextual output encoding for user-submitted content in posts and replies.

Recommended fix High confidence

4.0.5 for 4.x branch or 3.2.12 for 3.x branch

  1. Identify your current YAF.NET version by checking the application assembly version or admin panel
  2. Determine which major version branch you are currently using (3.x or 4.x)
  3. If on 3.x branch: upgrade to version 3.2.12 or later
  4. If on 4.x branch: upgrade to version 4.0.5 or later
  5. Backup your database and application files before upgrading
  6. Deploy the new version following standard upgrade procedures
  7. Verify the thread posting and reply features work correctly after upgrade
Caveat Upgrading major versions may introduce breaking changes; review release notes before proceeding

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,328.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-43939 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data