CVE-2021-34435 Remote code execution in Eclipse Theia
Attackers can achieve remote code execution by tricking users into previewing malicious HTML files in the Eclipse Theia mini-browser extension.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2021-34435?
CVE-2021-34435 is a high-severity code injection vulnerability in Eclipse Theia, published on 1 Sep 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
In Eclipse Theia 0.3.9 to 1.8.1, the "mini-browser" extension allows a user to preview HTML files in an iframe inside the IDE. But with the way it is made it is possible for a previewed HTML file to trigger an RCE. This exploit only happens if a user previews a malicious file..
Which versions are affected by CVE-2021-34435?
2 open source packages ship an affected version, including @theia/mini-browser. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
@theia/mini-browser npm | From 0.3.9 | 1.9.0 |
@theia/mini-browser npm | From 0.3.9 | 1.9.0 |
Products include Eclipse Theia.
How do I fix CVE-2021-34435?
Upgrade @theia/mini-browser to 1.9.0 or later.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2021-34435 being exploited?
There is no known exploitation of CVE-2021-34435 in the wild and no public exploit code.
Other vulnerabilities in Eclipse Theia
- CVE-2021-34436 XML external entity in Eclipse Theia
- CVE-2020-27224 Cross-site Scripting (XSS) in Eclipse Theia
- CVE-2026-60009 File upload in Eclipse Theia
- CVE-2026-44688 [Eclipse Theia] Indirect Prompt Injection via Adversarial Workspace File and Directory Names in AI Chat
- CVE-2026-44691 [Eclipse Theia] Arbitrary Command Execution via Untrusted Workspace Task Definitions
Sources
Also known as GHSA-v9w2-v7j9-rjpr.