CVE-2021-21320

User content sandbox can be confused into opening arbitrary documents

MEDIUM
4.3
CVSS Score
Published: March 2, 2021 at 02:45 AM UTC
Updated: June 17, 2026 at 03:35 AM UTC
2 products affected across 2 vendorsMatrix React SDKMatrix React SDK

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Severity
MEDIUM4.3
Exploit prediction
EPSS 0.9%

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

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 3.15.0
Affected range stops below 3.15.0, so it looks safe — our inference, not a vendor statement
v < 3.15.0
Affected range stops below 3.15.0, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
NONE
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-345

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