# CVE-2021-21320: User content sandbox can be confused into opening arbitrary documents

> Attackers can trick users into opening unexpected documents via sandbox confusion, though sensitive data remains protected.

- **Severity:** Low 2.6 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 2 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-52mq-6jcv-j79x

## What is CVE-2021-21320?

CVE-2021-21320 is a low-severity vulnerability in matrix-org matrix-react-sdk, published on 2 Mar 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

matrix-react-sdk is an npm package which is a Matrix SDK for React Javascript. In matrix-react-sdk before version 3.15.0, the user content sandbox can be abused to trick users into opening unexpected documents. The content is opened with a `blob` origin that cannot access Matrix user data, so messages and secrets are not at risk. This has been fixed in version 3.15.0.

Weakness: CWE-345 (Insufficient Verification of Data Authenticity)

## Which versions are affected by CVE-2021-21320?

2 open source packages ship an affected version, including matrix-react-sdk. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `matrix-react-sdk` | npm | All versions | 3.15.0 |
| `matrix-react-sdk` | npm | All versions | 3.15.0 |

Products: Matrix-React-Sdk Project Matrix-React-Sdk.

## How do I fix CVE-2021-21320?

Upgrade matrix-react-sdk to 3.15.0 or later.

## Is CVE-2021-21320 being exploited?

There is no known exploitation of CVE-2021-21320 in the wild and no public exploit code.

## Other vulnerabilities in matrix-org matrix-react-sdk

- [CVE-2023-28103](https://insights.sbomify.com/CVE-2023-28103/): Prototype pollution in matrix-react-sdk (high 8.2)
- [CVE-2023-37259](https://insights.sbomify.com/CVE-2023-37259/): Cross site scripting in Export Chat feature (medium 6.1)
- [CVE-2023-30609](https://insights.sbomify.com/CVE-2023-30609/): matrix-react-sdk vulnerable to HTML injection in search results via plaintext message highlighting (medium 5.4)
- [CVE-2021-32622](https://insights.sbomify.com/CVE-2021-32622/): File upload local preview can run embedded scripts after user interaction (medium 4.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21320 and fix it if it is affected.

What it is: CVE-2021-21320 is a low-severity vulnerability in matrix-org matrix-react-sdk, published on 2 Mar 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-21320 in the wild and no public exploit code.

Affected packages and fixed versions:
- matrix-react-sdk (npm): affected all versions; fixed in 3.15.0
- matrix-react-sdk (npm): affected all versions; fixed in 3.15.0

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-2021-21320/ (Markdown: https://insights.sbomify.com/CVE-2021-21320/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21320
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21320
- OSV: https://osv.dev/vulnerability/CVE-2021-21320

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21320/
Summaries are generated and may contain mistakes; the official description above is the record.