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Fencer Vulns
high 8.8

CVE-2021-34435 json

Remote code execution in Eclipse Theia

published 2021-09-01 5 y ago modified 2026-06-17 4 mo ago also GHSA-v9w2-v7j9-rjpr , EUVD-2021-2115

cvss
8.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 48%
public exploits
0
none known

Summary

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..

Patch / fix

  • npm @theia/mini-browser 1.9.0

Exploit prediction

0.60% chance of exploitation in the next 30 days, higher than 48% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugs.eclipse.org https://bugs.eclipse.org/bugs/show_bug.cgi?id=568018 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
NVD 2.0 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P
GitHub 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
npm @theia/mini-browser
>=0.3.9, <1.9.0
1.9.0

Affected products

  • The Eclipse Foundation Eclipse Theia

Classification

Weakness
  • CWE-942 Permissive Cross-domain Security Policy with Untrusted Domains
  • CWE-346 Origin Validation Error
  • CWE-668 Exposure of Resource to Wrong Sphere

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.