CVE-2021-21393

Denial of service (via resource exhaustion) due to improper input validation on groups/communities endpoints

Published Apr 12, 2021 CVSS 3.1 · 5.3 Medium EPSS 1.6% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
EUVD EUVD EUVD-2021-0129 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.
Github GHSA Github GHSA GHSA-jrh7-mhhx-6h88 Denial of service (via resource exhaustion) due to improper input validation on groups/communities endpoints
History

No history.

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Aug 3, 2024, 6:09 PM
Reserved
Dec 22, 2020, 12:00 AM
Status
Modified
Published
Apr 12, 2021, 10:15 PM
Modified
Jun 17, 2026, 3:35 AM