CVE-2021-34435 is a high-severity (CVSS 8.8) CWE-942 vulnerability in @theia/mini-browser. 1 public exploit reference exists, so weaponization risk is real. A fix is available for @theia/mini-browser — see the affected versions and patch details below.
Remote code execution in Eclipse Theia
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-34435 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@theia/mini-browsernpmDescription
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..
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @theia/mini-browser | ≥ 0.3.9&&< 1.9.0 | 1.9.0npm install @theia/mini-browser@1.9.0 |
Affected Products
theiaeclipseResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @theia/mini-browser, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @theia/mini-browser to 1.9.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-34435 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2021-34435 in your dependencies?
Find it across npm, including transitive dependencies.