cve.bz

CVE-2021-21274

6.5 mediumEPSS 2.2%

Medium (6.5). EPSS 2.2% chance of exploitation in the next 30 days. Fixed in matrix-synapse 1.25.0.

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 1.25.0, a malicious homeserver could redirect requests to their .well-known file to a large file. This can lead to a denial of service attack where homeservers will consume significantly more resources when requesting the .well-known file of a malicious homeserver. This affects any server which accepts federation requests from untrusted servers. Issue is resolved in version 1.25.0. As a workaround the `federation_domain_whitelist` setting can be used to restrict the homeservers communicated with over federation.

Severity

CVSS 3.1

6.5 medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
EPSS
2.2% chance of exploitation in the next 30 days; higher than 82% of CVEs (scores of 2026-10-31)
CWEs
CWE-770, CWE-400
Published
Modified
Record from
the NVD, synced

Affected

Packages (OSV)

AdvisoryEcosystemPackageAffectedFixed in
GHSA-2hwx-mjrm-v3g8PyPImatrix-synapse>=0.99.0 <1.25.01.25.0
PYSEC-2021-132PyPImatrix-synapse>=0.99.0 <1.25.01.25.0

References

Check your stackJSON