CVE-2021-35210
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 · uneditedContao 4.5.x through 4.9.x before 4.9.16, and 4.10.x through 4.11.x before 4.11.5, allows XSS. It is possible to inject code into the tl_log table that will be executed in the browser when the system log is called in the back end.
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 confidenceContao CMS versions 4.5.x through 4.9.x before 4.9.16 and 4.10.x through 4.11.x before 4.11.5 contain a stored cross-site scripting (XSS) vulnerability. Attackers can inject malicious JavaScript code into the tl_log database table, which executes in the browser of administrators when viewing the system log in the back end.
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>= 4.5.0, < 4.9.16>= 4.10.0, < 4.11.5CVSS 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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Identify the installed Contao versionLocate the version file or check the composer.json file in your Contao installation directory to determine the exact version numberAffected if The version is 4.5.0 through 4.9.15, or 4.10.0 through 4.11.4
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Verify the system log module is enabledCheck the Contao back-end settings or configuration files to confirm the system log feature is activeAffected if The system log module is enabled and accessible to administrators
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Inspect the tl_log database table for suspicious entriesQuery the tl_log table in your Contao database to look for entries containing script tags, javascript: URLs, or other XSS payload patternsAffected if The table contains unexpected entries with JavaScript code or HTML tags that were not legitimately generated by the system
You are affected if your Contao installation version falls within the vulnerable ranges (4.5.0-4.9.15 or 4.10.0-4.11.4) and the system log feature is accessible to backend users.
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 data4.9.164.11.5
Upgrade Contao to version 4.9.16 or 4.11.5 or later. As a workaround, restrict administrative access and disable logging of user-supplied input until the patch can be applied.
- Consultation2.0 h
- Implementation3.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-35210 — 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-2021-35210 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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- 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