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CVE-2021-21274

Published: 26 February 2021

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.

Priority

Medium

Cvss 3 Severity Score

6.5

Score breakdown

Status

Package Release Status
matrix-synapse
Launchpad, Ubuntu, Debian
bionic Needs triage

focal Needs triage

groovy Ignored
(end of life)
hirsute Not vulnerable
(1.26.0-3)
impish Not vulnerable
(1.26.0-3)
jammy Not vulnerable
(1.26.0-3)
kinetic Not vulnerable
(1.26.0-3)
lunar Not vulnerable
(1.26.0-3)
mantic Not vulnerable
(1.26.0-3)
noble Not vulnerable
(1.26.0-3)
trusty Does not exist

upstream
Released (1.25.0-1)
xenial Does not exist

Severity score breakdown

Parameter Value
Base score 6.5
Attack vector Network
Attack complexity Low
Privileges required None
User interaction Required
Scope Unchanged
Confidentiality None
Integrity impact None
Availability impact High
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H