vulnerability
Ubuntu: (CVE-2021-21394): matrix-synapse vulnerability
| Severity | CVSS | Published | Added | Modified |
|---|---|---|---|---|
| 4 | (AV:N/AC:L/Au:S/C:N/I:N/A:P) | Apr 12, 2021 | Jun 26, 2025 | Aug 18, 2025 |
Description
Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.28.0 Synapse is missing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion. Note that the groups feature is not part of the Matrix specification and the chosen maximum lengths are arbitrary. Not all clients might abide by them. Refer to referenced GitHub security advisory for additional details including workarounds.
Solution
References
- CVE-2021-21394
- https://attackerkb.com/topics/CVE-2021-21394
- CWE-20
- URL-https://github.com/matrix-org/synapse/pull/9321
- URL-https://github.com/matrix-org/synapse/pull/9393
- URL-https://github.com/matrix-org/synapse/security/advisories/GHSA-w9fg-xffh-p362
- URL-https://pypi.org/project/matrix-synapse/
- URL-https://www.cve.org/CVERecord?id=CVE-2021-21394
Explore Exposure Command
Confidently identify and prioritize exposures from endpoint to cloud with full attack surface visibility and threat-aware risk context.