CVE-2021-34436
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 · uneditedIn Eclipse Theia 0.1.1 to 0.2.0, it is possible to exploit the default build to obtain remote code execution (and XXE) via the theia-xml-extension. This extension uses lsp4xml (recently renamed to LemMinX) in order to provide language support for XML. This is installed by default.
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 confidenceRCE and XXE vulnerability in Eclipse Theia's default theia-xml-extension, which uses lsp4xml (now LemMinX) for XML language support. The vulnerability allows attackers to achieve remote code execution through XML external entity injection in the XML parser used by the extension.
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>= 0.1.1, <= 0.2.0CVSS 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
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/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 Eclipse Theia installation and versionLocate the Theia installation directory or check package.json for the @theia/core version. Run 'npm list @theia/core' or check the installed package version in your node_modules if using npm-based installation.Affected if The installed version is >= 0.1.1 and <= 0.2.0
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Verify theia-xml-extension is presentCheck if the package @theia/xml-extension or theia-xml-extension exists in node_modules, package.json dependencies, or the extensions directory of your Theia installation.Affected if The theia-xml-extension package is installed and enabled in the environment
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Confirm XML language server is activeCheck if the XML language server (lsp4xml/LemMinX) is running or loaded. This can be verified by examining active language servers in the Theia process or checking for xml language server processes.Affected if The XML language server is running as part of the Theia IDE instance
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Check for external entity resolution capabilityInspect XML parser settings in the lsp4xml/LemMinX configuration files within the theia-xml-extension. Look for settings related to external entity processing or XXE protection.Affected if External entity resolution is not explicitly disabled in the XML parser configuration
A user is affected if Eclipse Theia version is between 0.1.1 and 0.2.0 inclusive AND the theia-xml-extension with its XML language server is installed and active.
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 dataUpdate Eclipse Theia beyond version 0.2.0 or remove/disable the theia-xml-extension if XML functionality is not required.
- Consultation3.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-34436 — 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-2021-34436 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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