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Synapse V2 state resolution weakness allows Denial of Service (DoS)

Moderate severity GitHub Reviewed Published Apr 23, 2024 in element-hq/synapse • Updated May 4, 2024

Package

pip matrix-synapse (pip)

Affected versions

< 1.105.1

Patched versions

1.105.1

Description

Impact

A remote Matrix user with malicious intent, sharing a room with Synapse instances before 1.105.1, can dispatch specially crafted events to exploit a weakness in how the auth chain cover index is calculated. This can induce high CPU consumption and accumulate excessive data in the database of such instances, resulting in a denial of service.

Servers in private federations, or those that do not federate, are not affected.

Patches

Server administrators should upgrade to 1.105.1 or later.

Workarounds

One can:

  • ban the malicious users or ACL block servers from the rooms; and/or
  • leave the room and purge the room using the admin API

For more information

If you have any questions or comments about this advisory, please email us at security AT element.io.

References

@erikjohnston erikjohnston published to element-hq/synapse Apr 23, 2024
Published by the National Vulnerability Database Apr 23, 2024
Published to the GitHub Advisory Database Apr 23, 2024
Reviewed Apr 23, 2024
Last updated May 4, 2024

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS score

0.044%
(11th percentile)

Weaknesses

CVE ID

CVE-2024-31208

GHSA ID

GHSA-3h7q-rfh9-xm4v

Source code

Credits

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