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.

Category

5.3
CVSS
Severity: Medium
CVSS 3.1 •
CVSS 2.0 •
EPSS 0.55%
Vendor Advisory fedoraproject.org
Affected: matrix-org synapse
Published at:
Updated at:

References

Link Tags
https://pypi.org/project/matrix-synapse/ product third party advisory
https://github.com/matrix-org/synapse/pull/9321 third party advisory patch
https://github.com/matrix-org/synapse/pull/9393 third party advisory patch
https://github.com/matrix-org/synapse/security/advisories/GHSA-jrh7-mhhx-6h88 third party advisory patch
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/ vendor advisory

Frequently Asked Questions

What is the severity of CVE-2021-21393?
CVE-2021-21393 has been scored as a medium severity vulnerability.
How to fix CVE-2021-21393?
To fix CVE-2021-21393, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2021-21393 being actively exploited in the wild?
As for now, there are no information to confirm that CVE-2021-21393 is being actively exploited. According to its EPSS score, there is a ~1% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2021-21393?
CVE-2021-21393 affects matrix-org synapse.
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