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Cross-site Scripting (XSS)Weakness · CWE-79

CVE-2026-39935

MEDIUM · 6.9 CVSS v4.0 Published 2026-04-07
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
78/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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
Improper neutralization of input during web page generation ('cross-site scripting') vulnerability in The Wikimedia Foundation Mediawiki - CampaignEvents Extension allows Cross-Site Scripting (XSS). This issue was remediated only on the `master` branch.

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

Cross-site scripting (XSS) vulnerability in MediaWiki's CampaignEvents extension allows attackers to inject malicious scripts through improperly neutralized user input that gets rendered in web pages. This is a stored/reflected XSS issue where input validation or output encoding is insufficient.

MitigationUpdate to the patched version from the master branch or apply the specific fix to the CampaignEvents extension. Until patched, consider disabling the extension or implementing input filtering as a temporary workaround.

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
None
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:L/SI:L/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

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. Verify CampaignEvents extension is enabled
    Check your MediaWiki configuration files (e.g., LocalSettings.php) for lines containing 'CampaignEvents' or look for the extension in your /extensions/ directory
    Affected if The CampaignEvents extension is present and loaded in your MediaWiki installation
  2. Identify CampaignEvents extension version
    Check the extension's version file or composer.json in /extensions/CampaignEvents/, or look at the version metadata returned by MediaWiki's Special:Version page
    Affected if The installed version predates the security fix in the master branch and is not yet patched
  3. Confirm web access to CampaignEvents functionality
    Attempt to access CampaignEvents pages or features via the web interface (e.g., Special:CampaignEvents or related pages)
    Affected if The CampaignEvents web interface is accessible to users, allowing them to submit input that gets rendered without proper sanitization
  4. Inspect rendered output for user input handling
    Submit test input containing HTML/script characters through CampaignEvents forms and inspect the page source to see if input is reflected unescaped
    Affected if User-supplied input in CampaignEvents appears in the rendered HTML without being escaped or sanitized

You are affected if CampaignEvents extension is enabled and the installed version is older than the patched master branch version, with user input fields accessible via the web interface.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Update to the patched version from the master branch or apply the specific fix to the CampaignEvents extension. Until patched, consider disabling the extension or implementing input filtering as a temporary workaround.

Have this fixed Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,980
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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-2026-39935 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
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