CVE-2021-37626
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 is an open source CMS that allows you to create websites and scalable web applications. In affected versions it is possible to load PHP files by entering insert tags in the Contao back end. Installations are only affected if they have untrusted back end users who have the rights to modify fields that are shown in the front end. Update to Contao 4.4.56, 4.9.18 or 4.11.7 to resolve. If you cannot update then disable the login for untrusted back end users.
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 prior to 4.4.56, 4.9.18, and 4.11.7 contain a file inclusion vulnerability where untrusted authenticated backend users can load arbitrary PHP files through insert tags. This allows authenticated attackers to potentially achieve remote code execution by including malicious PHP files accessible through the CMS.
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>= 4.4.0, < 4.4.56>= 4.9.0, < 4.9.18>= 4.11.0, < 4.11.7= 4.0.0= 4.1.0= 4.2.0= 4.3.0= 4.5.0= 4.6.0= 4.7.0= 4.8.0= 4.10.0CVSS 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
- High
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
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 Contao versionCheck the composer.json file in the Contao installation root for the 'contao/core-bundle' version, or access the Contao Manager and look at the system information. The version may also be visible in the backend under 'System > Settings' or by checking the installed Contao version through the command line: 'composer show contao/core-bundle'Affected if The installed version falls within 4.4.0 to 4.4.55, 4.9.0 to 4.9.17, 4.11.0 to 4.11.6, or matches any of 4.0.0, 4.1.0, 4.2.0, 4.3.0, 4.5.0, 4.6.0, 4.7.0, 4.8.0, or 4.10.0
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Verify backend user accounts existAccess the Contao backend and navigate to 'Users > Users' or 'Users > Groups' to list all backend users and groups. Check if any user accounts are present beyond the initial administrator.Affected if There are any backend user accounts besides the main administrator, particularly users who have access to modify frontend-displayed content
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Confirm insert tags are in useSearch the Contao database or templates for the presence of insert tags (syntax like {{insert_tag_name::parameter}}). Check content elements, articles, or page layouts that may contain these tags, especially those that can be edited by non-administrator backend users.Affected if Insert tags are used in any content that can be edited by authenticated backend users who are not administrators
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Check file system permissionsExamine the web root directory for any writable PHP files that could be included. Look in folders like /files, /assets, or any custom upload directories accessible from the web. Verify which files the web server process can read.Affected if There are PHP files in accessible web directories that could be included by an attacker with backend access to modify content containing insert tags
You are affected if your Contao installation version is within the affected ranges AND you have authenticated backend users (other than the main admin) who can edit content containing insert tags.
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.
dbcve · scoped4.4.564.9.184.11.7
Update Contao to version 4.4.56, 4.9.18, or 4.11.7. If updates cannot be applied immediately, disable login access for untrusted backend users who have rights to modify frontend-displayed fields.
Contao 4.4.56 (for 4.4.x), 4.9.18 (for 4.9.x), or 4.11.7 (for 4.11.x)
- Identify your current Contao version in the back end (in the header area or via system/contao/manager-bundle composer.json)
- Determine your upgrade path: if using 4.4.x series, upgrade to 4.4.56; if using 4.9.x series, upgrade to 4.9.18; if using 4.11.x series, upgrade to 4.11.7; if using 4.0.0, upgrade to 4.4.56 (LTS stable branch)
- Create a full backup of your Contao installation including files and database
- If using Composer: run 'composer require contao/core-bundle:4.4.56' (or appropriate version) to update; if using the Contao Manager: use the GUI to select and install the target version
- After upgrade, clear all Contao caches via system/clear-cache or CLI (vendor/bin/contao-console cache:clear --all)
- Verify the back end is accessible and functionality works as expected
- If you cannot upgrade immediately and have untrusted back end users, disable their accounts or revoke their permissions to modify front-end-displayed fields as a temporary mitigation
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation3.0 h
- Testing2.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-37626 — 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-2021-37626 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
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