CVE-2026-12609 Path traversal in Eclipse Theia

High 7.5 Published 5 Aug 2026 Updated 5 Aug 2026

An unauthenticated attacker can exploit a path traversal vulnerability in Eclipse Theia to read arbitrary files from the server.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-12609?

CVE-2026-12609 is a high-severity path traversal vulnerability in Eclipse Theia, published on 5 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

In Eclipse Theia versions 1.66.0 and up until including 1.73.1, the `@theia/plugin-ext` backend exposes the `/hostedPlugin/:pluginId/:path(*)` HTTP endpoint, which resolves the requested file path with `path.resolve(localPath, filePath)` without verifying that the resolved path stays within the plugin's directory. An unauthenticated network attacker can send percent-encoded `../` sequences (`%2e%2e%2f`) that decode into the path parameter and escape the plugin directory, allowing arbitrary files readable by the Theia backend process to be retrieved. Plugin IDs are derived deterministically from a plugin's publisher and name, so built-in plugins serve as reliable anchors that require no prior knowledge of the target system.

Weakness: CWE-22

Which versions are affected by CVE-2026-12609?

It affects 1 product.

Products include Eclipse Theia.

How do I fix CVE-2026-12609?

No fix has been published for CVE-2026-12609 yet. Limit exposure of the affected software until one is available.

Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.

Is CVE-2026-12609 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-12609 exists.

Public exploit code: 1 Nuclei template.

Sources

Also known as GHSA-34gw-v4cc-pv7c, GHSA-qmm6-p8q4-2g48.