#VU56488 Information disclosure in Matrix Javascript SDK - CVE-2021-40823

Vulnerability identifier: #VU56488

Vulnerability risk: Medium

CVSSv4.0: 4.6 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2021-40823

CWE-ID: CWE-200

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Matrix Javascript SDK
Web applications / JS libraries

Vendor: Matrix.org

Description

The vulnerability allows a remote attacker to gain access to sensitive information.

The vulnerability exists due to logic error in the room key sharing functionality in matrix-js-sdk. In certain circumstances it is possible to trick vulnerable clients into disclosing encryption keys for messages previously sent by that client to user accounts later compromised by an attacker.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Matrix Javascript SDK: 0.1.0 - 12.4.0

---

External links
https://github.com/matrix-org/matrix-js-sdk/releases/tag/v12.4.1
https://matrix.org/blog/2021/09/13/vulnerability-disclosure-key-sharing
https://github.com/matrix-org/matrix-js-sdk/security/advisories/GHSA-23cm-x6j7-6hq3

---

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.