# CVE-2026-12609: Path traversal in Eclipse Theia

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

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 5 Aug 2026
- **Updated:** 5 Aug 2026
- **Also known as:** GHSA-34gw-v4cc-pv7c, GHSA-qmm6-p8q4-2g48

## 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 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-12609?

It affects 1 product.


Products: 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.

## 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:

- Eclipse Theia - Unauthenticated Path Traversal (nuclei): http/cves/2026/CVE-2026-12609.yaml

## Other vulnerabilities in Eclipse Theia

- [CVE-2021-34436](https://insights.sbomify.com/CVE-2021-34436/): XML external entity in Eclipse Theia (critical 9.8)
- [CVE-2020-27224](https://insights.sbomify.com/CVE-2020-27224/): Cross-site Scripting (XSS) in Eclipse Theia (critical 9.6)
- [CVE-2026-60009](https://insights.sbomify.com/CVE-2026-60009/): File upload in Eclipse Theia (high 8.8)
- [CVE-2021-34435](https://insights.sbomify.com/CVE-2021-34435/): Remote code execution in Eclipse Theia (high 8.8)
- [CVE-2026-44688](https://insights.sbomify.com/CVE-2026-44688/): [Eclipse Theia] Indirect Prompt Injection via Adversarial Workspace File and Directory Names in AI Chat (high 8.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-12609 and fix it if it is affected.

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

Affected product: Eclipse Theia. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-12609/ (Markdown: https://insights.sbomify.com/CVE-2026-12609/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-12609
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-12609
- OSV: https://osv.dev/vulnerability/CVE-2026-12609

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-12609/
Summaries are generated and may contain mistakes; the official description above is the record.