CVE-2021-34435Public exploitNetwork attack vector

Remote code execution via same-origin HTML preview

Published Sep 1, 2021 · Updated Aug 4, 2024

Remote code execution in Eclipse Theia 0.3.9 through 1.8.1 allows remote attackers to run backend commands via a malicious HTML preview. The mini-browser serves previewed HTML in an iframe with scripts and same-origin access, letting its script open the backend WebSocket and call terminal services. Execution requires a user to preview the attacker-controlled file and activate its payload, after which commands run with the Theia backend process's privileges.

CVSS severity8.8
High
EPSS probability0.60%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Remote code execution in Eclipse Theia 0.3.9 through 1.8.1 allows remote attackers to run backend commands via a malicious HTML preview. The mini-browser serves previewed HTML in an iframe with scripts and same-origin access, letting its script open the backend WebSocket and call terminal services. Execution requires a user to preview the attacker-controlled file and activate its payload, after which commands run with the Theia backend process's privileges.

The record

CVE
CVE-2021-34435
Published
Sep 1, 2021
Updated
Aug 4, 2024
Vendor
The Eclipse Foundation
Product
Eclipse Theia
Classifications
CWE-346, CWE-942, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 1, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0.3.9 <unspecified
  2. Affected versionversion=unspecified <=1.8.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Eclipse Foundation · Eclipse Theiaversion=0.3.9 <unspecified; version=unspecified <=1.8.1

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-346Origin Validation Error
CWE-942Permissive Cross-domain Policy with Untrusted Domains
T1204.002Malicious File

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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