CVE-2021-21274

MITRE NVD CVE.ORG Print: PDF PDF

Summary

CVECVE-2021-21274
StatePUBLIC
Assigner[email protected]
Source PriorityCVE Program / NVD first with legacy fallback
Published2021-02-26 18:15:00 UTC
Updated2023-11-07 03:29:00 UTC
DescriptionSynapse 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.

Risk And Classification

Problem Types: CWE-770

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Fedoraproject Fedora 34 All All All
Application Matrix Synapse All All All All
Application Matrix Synapse All All All All

References

ReferenceSourceLinkTags
Release v1.25.0 · matrix-org/synapse · GitHub MISC github.com Third Party Advisory
Add a maximum size for well-known lookups. (#8950) · matrix-org/synapse@ff5c4da · GitHub MISC github.com Patch, Third Party Advisory
[SECURITY] Fedora 34 Update: matrix-synapse-1.38.1-1.fc34 - package-announce - Fedora Mailing-Lists lists.fedoraproject.org
Denial of service attack via .well-known lookups · Advisory · matrix-org/synapse · GitHub CONFIRM github.com Patch, Third Party Advisory
Add a maximum size for well-known lookups. by clokep · Pull Request #8950 · matrix-org/synapse · GitHub MISC github.com Patch, Third Party Advisory
[SECURITY] Fedora 34 Update: matrix-synapse-1.38.1-1.fc34 - package-announce - Fedora Mailing-Lists FEDORA lists.fedoraproject.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Legacy QID Mappings

  • 281765 Fedora Security Update for matrix (FEDORA-2021-a627cfd31e)
  • 981372 Python (pip) Security Update for matrix-synapse (GHSA-2hwx-mjrm-v3g8)
© CVE.report 2026 |

Use of this information constitutes acceptance for use in an AS IS condition. There are NO warranties, implied or otherwise, with regard to this information or its use. Any use of this information is at the user's risk. It is the responsibility of user to evaluate the accuracy, completeness or usefulness of any information, opinion, advice or other content. EACH USER WILL BE SOLELY RESPONSIBLE FOR ANY consequences of his or her direct or indirect use of this web site. ALL WARRANTIES OF ANY KIND ARE EXPRESSLY DISCLAIMED. This site will NOT BE LIABLE FOR ANY DIRECT, INDIRECT or any other kind of loss.

CVE, CWE, and OVAL are registred trademarks of The MITRE Corporation and the authoritative source of CVE content is MITRE's CVE web site. This site includes MITRE data granted under the following license.

CVE.report and Source URL Uptime Status status.cve.report