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Denial of service attack via .well-known lookups

Moderate severity GitHub Reviewed Published Feb 25, 2021 in matrix-org/synapse • Updated Jan 29, 2023

Package

pip matrix-synapse (pip)

Affected versions

>= 0.99.0, < 1.25.0

Patched versions

1.25.0

Description

Impact

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.

Patches

Issue is resolved by #8950. A bug not affecting the security aspects of this was fixed in #9108.

Workarounds

The federation_domain_whitelist setting can be used to restrict the homeservers communicated with over federation.

References

@clokep clokep published to matrix-org/synapse Feb 25, 2021
Published by the National Vulnerability Database Feb 26, 2021
Reviewed Mar 1, 2021
Published to the GitHub Advisory Database Mar 1, 2021
Last updated Jan 29, 2023

Severity

Moderate
4.3
/ 10

CVSS base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L

Weaknesses

CVE ID

CVE-2021-21274

GHSA ID

GHSA-2hwx-mjrm-v3g8

Source code

Credits

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