CVE-2021-21393
Denial of service (via resource exhaustion) due to improper input validation on groups/communities endpoints
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.
How to fix CVE-2021-21393
To remediate CVE-2021-21393, upgrade the affected package to a fixed version below.
- —upgrade to 1.28.0-1 or later
- —upgrade to 1.28.0 or later
- —upgrade to 1.28.0 or later
Is CVE-2021-21393 being exploited?
Low — EPSS is 0.5%, meaning exploitation activity has not been observed at scale.
Affected packages (3)
- from 0, < 1.28.0-1
- from 0, < 1.28.0
- from 0, < 1.28.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N |
| osv | CVSS 3.1 | MEDIUM5.3 | CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H |