How severe is CVE-2021-34436?

CVE-2021-34436 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-34436 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (81st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-34436?

CVE-2021-34436 affects Eclipse Theia. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-34436?

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

When was CVE-2021-34436 published?

CVE-2021-34436 was published on 2021-09-02 and last updated on 2026-06-17.

CVE-2021-34436

CVE-2021-34436 is a critical-severity vulnerability in Eclipse Theia with a CVSS 3.x base score of 9.8. 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-22.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 2% (81st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-22
Affected product: Eclipse Theia
Published: 2021-09-02
Last modified: 2026-06-17

Description

In Eclipse Theia 0.1.1 to 0.2.0, it is possible to exploit the default build to obtain remote code execution (and XXE) via the theia-xml-extension. This extension uses lsp4xml (recently renamed to LemMinX) in order to provide language support for XML. This is installed by default.

Frequently asked questions

What is CVE-2021-34436?: In Eclipse Theia 0.1.1 to 0.2.0, it is possible to exploit the default build to obtain remote code execution (and XXE) via the theia-xml-extension. This extension uses lsp4xml (recently renamed to LemMinX) in order to provide language support for XML. This is installed by default.
How severe is CVE-2021-34436?: CVE-2021-34436 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-34436 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (81st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-34436?: CVE-2021-34436 affects Eclipse Theia. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-34436?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-34436 published?: CVE-2021-34436 was published on 2021-09-02 and last updated on 2026-06-17.

References

https://bugs.eclipse.org/bugs/show_bug.cgi?id=563174

Affected products (1)

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

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