What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-03-02 · updated 2026-06-17
• Weakness: CWE-345

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.

Affected products

• matrix-org matrix-react-sdk: before 3.15.0 — fixed in 3.15.0

How to fix

Upgrade to a fixed version: matrix-org matrix-react-sdk 3.15.0. Check the vendor advisory for mitigations.

References

• https://github.com/matrix-org/matrix-react-sdk/commit/b386f0c73b95ecbb6ea7f8f79c6ff5171a8dedd1
• https://github.com/matrix-org/matrix-react-sdk/pull/5657
• https://github.com/matrix-org/matrix-react-sdk/security/advisories/GHSA-52mq-6jcv-j79x
• https://www.npmjs.com/package/matrix-react-sdk
• https://github.com/matrix-org/matrix-react-sdk/commit/b386f0c73b95ecbb6ea7f8f79c6ff5171a8dedd1
• https://github.com/matrix-org/matrix-react-sdk/pull/5657
• https://github.com/matrix-org/matrix-react-sdk/security/advisories/GHSA-52mq-6jcv-j79x
• https://www.npmjs.com/package/matrix-react-sdk

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