Uncontrolled Resource Consumption in Matrix Synapse
Impact
Synapse before 1.52.0 with URL preview functionality enabled will attempt to generate URL previews for media stream URLs without properly limiting connection time. Connections will only be terminated after max_spider_size (default: 10M) bytes have been downloaded, which can in some cases lead to long-lived connections towards the streaming media server (for instance, Icecast).
This can cause excessive traffic and connections toward such servers if their stream URL is, for example, posted to a large room with many Synapse instances with URL preview enabled.
Patches
1.52.0 implements a timeout mechanism which will terminate URL preview connections after 30 seconds. Since generating URL previews for media streams is not supported and always fails, 1.53.0 additionally implements an allow list for content types for which Synapse will even attempt to generate a URL preview.
We recommend upgrading to 1.53.0 to fully resolve the issue.
Workarounds
Turn off URL preview functionality by setting url_preview_enabled: false in the Synapse configuration file.
References
- Patch (timeout): https://github.com/matrix-org/synapse/pull/11784
- Patch (content type allow list): https://github.com/matrix-org/synapse/pull/11936
For more information
If you have any questions or comments about this advisory, e-mail us at security@matrix.org.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | matrix-synapse | < 1.53.0 | 1.53.0 |
References
- https://github.com/matrix-org/synapse/security/advisories/GHSA-4822-jvwx-w47h
- https://nvd.nist.gov/vuln/detail/CVE-2022-41952
- https://github.com/matrix-org/synapse/pull/11784
- https://github.com/matrix-org/synapse/pull/11936
- https://github.com/matrix-org/synapse
- https://github.com/matrix-org/synapse/releases/tag/v1.52.0
- https://github.com/matrix-org/synapse/releases/tag/v1.53.0
- https://pypi.org/project/matrix-synapse
- https://github.com/advisories/GHSA-4822-jvwx-w47h
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L- Weakness (CWE)
CWE-400, CWE-772- Platform
- Python (PyPI)
- Package
matrix-synapse- Disclosed
- 01.04.2022
- Updated
- 11.10.2026 13:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-663 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-4822-jvwx-w47h - CC BY 4.0
Vulnerability history: matrix-synapse
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 45
- First → latest
- 03.2019 05.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 21
- Medium 21
- Low 3
Disclosures per year
- 2019: 3
- 2020: 3
- 2021: 12
- 2022: 7
- 2023: 9
- 2024: 7
- 2025: 2
- 2026: 2
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