# CVE-2020-27224: Cross-site Scripting (XSS) in Eclipse Theia

> Attackers can execute arbitrary code via the Markdown Preview feature in Eclipse Theia, posing a risk to developers using the IDE.

- **Severity:** Critical 9.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 24 Feb 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-gcm9-cc3r-c6vj

## What is CVE-2020-27224?

CVE-2020-27224 is a critical cross-site scripting vulnerability in Eclipse Theia, published on 24 Feb 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

In Eclipse Theia versions up to and including 1.2.0, the Markdown Preview (@theia/preview), can be exploited to execute arbitrary code.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2020-27224?

2 open source packages ship an affected version, including @theia/preview. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@theia/preview` | npm | All versions | 1.3.0 |
| `@theia/preview` | npm | All versions | 1.3.0 |

Products: Eclipse Theia.

## How do I fix CVE-2020-27224?

Upgrade @theia/preview to 1.3.0 or later.

## Is CVE-2020-27224 being exploited?

There is no known exploitation of CVE-2020-27224 in the wild and no public exploit code.

## 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-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)
- [CVE-2026-44691](https://insights.sbomify.com/CVE-2026-44691/): [Eclipse Theia] Arbitrary Command Execution via Untrusted Workspace Task Definitions (high 8.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-27224 and fix it if it is affected.

What it is: CVE-2020-27224 is a critical cross-site scripting vulnerability in Eclipse Theia, published on 24 Feb 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2020-27224 in the wild and no public exploit code.

Affected packages and fixed versions:
- @theia/preview (npm): affected all versions; fixed in 1.3.0
- @theia/preview (npm): affected all versions; fixed in 1.3.0

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-2020-27224/ (Markdown: https://insights.sbomify.com/CVE-2020-27224/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-27224
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-27224
- OSV: https://osv.dev/vulnerability/CVE-2020-27224

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-27224/
Summaries are generated and may contain mistakes; the official description above is the record.