What is CVE-2021-34435?

CVE-2021-34435 is a high-severity vulnerability in Eclipse Theia, classified under Permissive Cross-domain Policy with Untrusted Domains. CVSS score: 8.8/10. Published 2021-09-01.

How severe is CVE-2021-34435?

High severity. CVSS v3 base score is 8.8 out of 10.

Vulnerability in Eclipse Theia

CVE-2021-34435

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..

Published 2021-09-01 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.006 (46.4th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 46th percentile — 46.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000

Affected products

Eclipse Theia
The Eclipse Foundation Theia — versions 0.3.9, unspecified

Weakness classification (CWE)

References

bugs.eclipse.org/bugs/show_bug.cgi (Exploit, Patch, Vendor Advisory)

Frequently asked questions

What is CVE-2021-34435?: CVE-2021-34435 is a high-severity vulnerability in Eclipse Theia, classified under Permissive Cross-domain Policy with Untrusted Domains. CVSS score: 8.8/10. Published 2021-09-01.
How severe is CVE-2021-34435?: High severity. CVSS v3 base score is 8.8 out of 10.