Joomla\!Application · Joomla
CVE-2021-26030
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 · uneditedAn issue was discovered in Joomla! 3.0.0 through 3.9.25. Inadequate escaping allowed XSS attacks using the logo parameter of the default templates on error page
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 confidenceCross-site scripting (XSS) vulnerability in Joomla CMS versions 3.0.0 through 3.9.25. The logo parameter in default templates (Protostar and Beez3) is not properly escaped when rendered on error pages, allowing authenticated attackers to inject malicious JavaScript through the template's logo configuration.
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
Joomla\!Application
>= 3.0.0, <= 3.9.25CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Check Joomla versionNavigate to Help > System Information in the Joomla admin panel, or check the libraries/cms.php file for the VERSION constant, or look at the version.json file in the installation rootAffected if The installed version is >= 3.0.0 and <= 3.9.25
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Identify active default templateGo to Extensions > Templates > Styles in the admin panel and check which template is set as default for the site (specifically for the 'site' location)Affected if The default site template is either Protostar or Beez3
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Check template logo configurationGo to Extensions > Templates > Styles, edit the Protostar or Beez3 style, and inspect the 'Logo File' parameter in the template details tabAffected if A custom logo file path is configured in the template settings (the vulnerability triggers when a logo is set and an error page is displayed)
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Verify error page accessibilityTrigger an error condition (such as a 404 error) by accessing a non-existent page on the site to confirm error pages renderAffected if Error pages are accessible and render using the default template (Protostar or Beez3) with the configured logo parameter
You are affected if your Joomla installation runs version 3.0.0 through 3.9.25 and uses Protostar or Beez3 as the default template with a configured logo parameter on error pages.
Generated from the published advisory. Verify against your own configuration.
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 dataUpgrade Joomla to version 3.9.26 or later which includes proper escaping for the logo parameter on error pages. Alternatively, disable or restrict template parameter modifications to untrusted users.
Fix this in Joomla\!
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 h
- Testing2.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,848.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-26030 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-26030 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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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.
- 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