Synapse Matrix has a partial room state leak via Sliding Sync

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

EPSS

• CVE-2024-53867: 0.44% estimated exploitation activity in the next 30 days; percentile 38.50 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact 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. Patches Synapse version 1.120.1 fixes the problem. Workarounds Disable Sliding Sync. References https://github.com/matrix-org/matrix-spec-proposals/pull/4186 https://github.com/element-hq/synapse/blob/d80cd57c54427687afcb48740d99219c88a0fff1/synapse/config/experimental.py#L341-L344 For more information If you have any questions or comments about this advisory, please email us at security at element.io.

Published by the source

3 Dec 2024, 18:44 UTC

Last modified by the source

7 Jul 2026, 17:57 UTC

Source last checked

26 Oct 2026, 13:30 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-56w4-5538-8v8h

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-56w4-5538-8v8h

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# Patch Next advisory brief: CVE-2024-53867

Advisory: Synapse Matrix has a partial room state leak via Sliding Sync
IDs: CVE-2024-53867, GHSA-56w4-5538-8v8h
Record: https://patchnext.com/advisories/cve-2024-53867 (revision 2, source checked 26 Oct 2026, 13:30 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: matrix-synapse 1.120.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI matrix-synapse: affected >= 1.113.0rc1, < 1.120.1; fixed in 1.120.1

## Suggested inspection (read-only)
- `python -m pip show matrix-synapse`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on matrix-synapse.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-56w4-5538-8v8h (OSV record GHSA-56w4-5538-8v8h lists affected ranges: PyPI matrix-synapse >=1.113.0rc1 <1.120.1 (fixed))
- Verified: https://github.com/advisories/GHSA-56w4-5538-8v8h (GitHub-reviewed advisory GHSA-56w4-5538-8v8h lists affected ranges: PyPI matrix-synapse >=1.113.0rc1 <1.120.1)

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