How severe is CVE-2021-34435?

CVE-2021-34435 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-34435 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (44th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-34435?

CVE-2021-34435 affects Eclipse Theia. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-34435?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-34435 published?

CVE-2021-34435 was published on 2021-09-01 and last updated on 2026-06-17.

CVE-2021-34435

CVE-2021-34435 is a high-severity vulnerability in Eclipse Theia with a CVSS 3.x base score of 8.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-346.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v2: 6.8
EPSS exploit prediction: 1% (44th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-346
Affected product: Eclipse Theia
Published: 2021-09-01
Last modified: 2026-06-17

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..

Frequently asked questions

What is 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..
How severe is CVE-2021-34435?: CVE-2021-34435 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-34435 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (44th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-34435?: CVE-2021-34435 affects Eclipse Theia. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-34435?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-34435 published?: CVE-2021-34435 was published on 2021-09-01 and last updated on 2026-06-17.

References

https://bugs.eclipse.org/bugs/show_bug.cgi?id=568018

Affected products (1)

cpe:2.3:a:eclipse:theia:*:*:*:*:*:*:*:*

More vulnerabilities in Eclipse Theia

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CVE-2026-44688 — High (CVSS 8.8): In Eclipse Theia versions prior to 1.71.0, the AI chat agent processed workspace file and directory names as part of…
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