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National Vulnerability Database

National Vulnerability Database

NVD

National Vulnerability Database
  1. Vulnerabilities

CVE-2021-21274 Detail

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 1.25.0, 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.


Metrics

 
NVD enrichment efforts reference publicly available information to associate vector strings. CVSS information contributed by other sources is also displayed.
CVSS 4.0 Severity and Vector Strings:

NIST CVSS score
NIST: NVD
N/A
NVD assessment not yet provided.

References to Advisories, Solutions, and Tools

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URL Source(s) Tag(s)
https://github.com/matrix-org/synapse/commit/ff5c4da1289cb5e097902b3e55b771be342c29d6 CVE, GitHub, Inc. Patch  Third Party Advisory 
https://github.com/matrix-org/synapse/pull/8950 CVE, GitHub, Inc. Patch  Third Party Advisory 
https://github.com/matrix-org/synapse/releases/tag/v1.25.0 CVE, GitHub, Inc. Third Party Advisory 
https://github.com/matrix-org/synapse/security/advisories/GHSA-2hwx-mjrm-v3g8 CVE, GitHub, Inc. Patch  Third Party Advisory 
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/ CVE, GitHub, Inc.

Weakness Enumeration

CWE-ID CWE Name Source
CWE-770 Allocation of Resources Without Limits or Throttling cwe source acceptance level NIST  
CWE-400 Uncontrolled Resource Consumption GitHub, Inc.  

Known Affected Software Configurations Switch to CPE 2.2

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Change History

8 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2021-21274
NVD Published Date:
02/26/2021
NVD Last Modified:
06/16/2026
Source:
GitHub, Inc.