TYPO3CMS
CVE-2021-21359
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 · uneditedTYPO3 is an open source PHP based web content management system. In TYPO3 before versions 9.5.25, 10.4.14, 11.1.1 requesting invalid or non-existing resources via HTTP triggers the page error handler which again could retrieve content to be shown as error message from another page. This leads to a scenario in which the application is calling itself recursively - amplifying the impact of the initial attack until the limits of the web server are exceeded. This is fixed in versions 9.5.25, 10.4.14, 11.1.1.
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 confidenceIn TYPO3 before versions 9.5.25, 10.4.14, 11.1.1, requesting invalid or non-existing resources via HTTP triggers the page error handler which retrieves content from another page to display as an error message. This creates a recursive self-call that amplifies until web server limits are exceeded, causing denial of service.
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
TYPO3CMS
>= 9.0.0, < 9.5.25>= 10.0.0, < 10.4.14>= 11.0.0, < 11.1.1CVSS 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
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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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Determine installed TYPO3 versionCheck the VERSION file in the TYPO3 root directory, or look in composer.json under 'version', or access the TYPO3 Install Tool > AboutAffected if The installed version is 9.0.0 through 9.4.x, 9.5.0 through 9.5.24, 10.0.0 through 10.4.13, 11.0.0 through 11.1.0, or any 11.x version below 11.1.1
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Identify if page error handler is configuredIn TYPO3 backend, go to Site Management > Error Handling (or check the site's YAML configuration file for errorHandlers configuration). Look for 'showContentFromPage' or similar settings that fetch error content from another page.Affected if An error handler is configured to retrieve content from another page (the page error handler feature is enabled)
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Verify the site uses the built-in error handler for missing resourcesCheck the site's configuration (typically in config/sites/*/config.yaml) for settings like 'errorHandling' that route 404 or other error responses to a custom handler that pulls content from a page.Affected if The site configuration contains error handling rules that fetch content from a page ID for error responses
You are affected if your TYPO3 installation version falls within 9.0.0-9.5.24, 10.0.0-10.4.13, or 11.0.0-11.1.0 AND your site configuration uses the page error handler feature to display content from one page as error messages for missing resources.
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 data9.5.2510.4.1411.1.1
Upgrade TYPO3 to version 9.5.25, 10.4.14, 11.1.1 or later to resolve the recursive error handler vulnerability.
Fix this in TYPO3
Scoped from the published advisory
- Consultation3.0 h
- Implementation6.0 h
- Testing3.0 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 $3,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-21359 — 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-2021-21359 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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