# CVE-2021-34436: XML external entity in Eclipse Theia

> Attackers can achieve remote code execution and read sensitive data via XML External Entity injection in the default XML extension of Eclipse Theia.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 2 Sep 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-8gpx-73gc-wq7c

## What is CVE-2021-34436?

CVE-2021-34436 is a critical vulnerability in Eclipse Theia, published on 2 Sep 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In 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.

Weakness: CWE-611 (Improper Restriction of XML External Entity Reference), CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2021-34436?

It affects 1 product.


Products: Eclipse Theia.

## How do I fix CVE-2021-34436?

No fix has been published for CVE-2021-34436 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-34436 being exploited?

There is no known exploitation of CVE-2021-34436 in the wild and no public exploit code.

## Other vulnerabilities in Eclipse Theia

- [CVE-2020-27224](https://insights.sbomify.com/CVE-2020-27224/): Cross-site Scripting (XSS) in Eclipse Theia (critical 9.6)
- [CVE-2026-60009](https://insights.sbomify.com/CVE-2026-60009/): File upload in Eclipse Theia (high 8.8)
- [CVE-2021-34435](https://insights.sbomify.com/CVE-2021-34435/): Remote code execution in Eclipse Theia (high 8.8)
- [CVE-2026-44688](https://insights.sbomify.com/CVE-2026-44688/): [Eclipse Theia] Indirect Prompt Injection via Adversarial Workspace File and Directory Names in AI Chat (high 8.4)
- [CVE-2026-44691](https://insights.sbomify.com/CVE-2026-44691/): [Eclipse Theia] Arbitrary Command Execution via Untrusted Workspace Task Definitions (high 8.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-34436 and fix it if it is affected.

What it is: CVE-2021-34436 is a critical vulnerability in Eclipse Theia, published on 2 Sep 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-34436 in the wild and no public exploit code.

Affected product: Eclipse Theia. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-34436/ (Markdown: https://insights.sbomify.com/CVE-2021-34436/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-34436
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-34436
- OSV: https://osv.dev/vulnerability/CVE-2021-34436

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-34436/
Summaries are generated and may contain mistakes; the official description above is the record.