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URL previews of unusual or maliciously-crafted pages can crash Synapse media repositories or Synapse monoliths

Moderate severity GitHub Reviewed Published Jun 28, 2022 in matrix-org/synapse • Updated Jan 27, 2023

Package

pip matrix-synapse (pip)

Affected versions

< 1.61.1

Patched versions

1.61.1

Description

Impact

URL previews of some web pages can exhaust the available stack space for the Synapse process due to unbounded recursion.
This is sometimes recoverable and leads to an error for the request causing the problem, but in other cases the Synapse process may crash altogether.

It is possible to exploit this maliciously, either by malicious users on the homeserver, or by remote users sending URLs that a local user's client may automatically request a URL preview for.
Remote users are not able to exploit this directly, because the URL preview endpoint is authenticated.

Am I affected?

  • deployments with url_preview_enabled: false set in configuration are not affected.
  • deployments with url_preview_enabled: true set in configuration are affected.
  • deployments with no configuration value set for url_preview_enabled are not affected, because the default is false.

Patches

Administrators of homeservers with URL previews enabled are advised to upgrade to v1.61.1 or higher.

Workarounds

  • URL previews can be disabled in the configuration file by setting url_preview_enabled: false.
  • Deployments using workers can choose to offload URL previews to one or more dedicated worker(s), ensuring that a process crash does not disrupt other functionality of Synapse.

For more information

If you have any questions or comments about this advisory, e-mail us at [email protected].

References

@anoadragon453 anoadragon453 published to matrix-org/synapse Jun 28, 2022
Published by the National Vulnerability Database Jun 28, 2022
Published to the GitHub Advisory Database Jun 29, 2022
Reviewed Jun 29, 2022
Last updated Jan 27, 2023

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

0.136%
(50th percentile)

Weaknesses

CVE ID

CVE-2022-31052

GHSA ID

GHSA-22p3-qrh9-cx32

Source code

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