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XenforoApplication

CVE-2026-35055

MEDIUM · 6.1 CVSS v3.1 Published 2026-04-01
Fix available
A fix is available. Upgrade to 2.2.18 / 2.3.9 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges

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
XenForo before 2.3.9 and before 2.2.18 is vulnerable to cross-site scripting (XSS) related to lightbox usage in posts. An attacker can inject malicious scripts that execute when users interact with post content displayed in the lightbox.

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 · moderate confidence

Stored XSS vulnerability in XenForo where malicious JavaScript injected into post content executes when users view that content via the lightbox modal feature. The lightbox fails to properly sanitize post content before rendering it in the modal context, allowing script execution upon user interaction with lightbox-displayed posts.

MitigationUpgrade XenForo to version 2.3.9 or later (2.x branch) or 2.2.18 or later (2.2 branch) to patch the lightbox XSS vulnerability.

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

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
XenforoApplication
Affected:< 2.2.18>= 2.3.0, < 2.3.9

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
None
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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. Check XenForo version in admin panel
    Log into the XenForo admin control panel and navigate to Home > Dashboard or Statistics to view the installed XenForo version number.
    Affected if The version displayed is less than 2.2.18, or is 2.3.0 through 2.3.8 inclusive.
  2. Verify XenForo version via file
    Locate the src/version.php file in your XenForo installation directory and read the XF_VERSION constant to determine the installed version.
    Affected if The version shown is less than 2.2.18, or is 2.3.0 through 2.3.8 inclusive.
  3. Confirm lightbox feature is in use
    Examine your forum templates or configuration to determine if the lightbox modal feature is enabled for viewing post content and images.
    Affected if The lightbox feature is active and users can open posts or images in a modal view.
  4. Check for suspicious post content
    Query your database posts table for HTML or script tags within post content that could represent injected malicious code: SELECT * FROM xf_post WHERE message LIKE '%<script%' OR message LIKE '%javascript:%' OR message LIKE '%onload=%'.
    Affected if Posts exist containing script tags, javascript: URIs, or event handlers like onload that could execute when opened in the lightbox.

Your environment is affected if the installed XenForo version is below 2.2.18 or between 2.3.0 and 2.3.8, the lightbox feature is enabled, and user posts containing potentially malicious script content exist in the database.

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
Upgrade available Upgrade to 2.2.18 / 2.3.9 or later
Fixed in 2.2.182.3.9
Interim mitigation

Upgrade XenForo to version 2.3.9 or later (2.x branch) or 2.2.18 or later (2.2 branch) to patch the lightbox XSS vulnerability.

Recommended fix High confidence

XenForo 2.2.18 or XenForo 2.3.9 (depending on your current branch)

  1. Identify your current XenForo version by checking the admin control panel or version.php file
  2. If running XenForo 2.3.x series, upgrade to version 2.3.9 or later
  3. If running XenForo 2.2.x series, upgrade to version 2.2.18 or later
  4. After upgrading, verify the installed version matches the expected fixed release
  5. Clear any caches (including template caches) after the upgrade to ensure the patched code takes effect
Caveat Review XenForo release notes before upgrading; minor version upgrades typically maintain compatibility but custom add-ons or templates may require updates

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

Fix this in Xenforo Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.

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-2026-35055 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