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

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-12-03 · updated 2026-06-17
Weakness: CWE-497

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.

Affected products

matrix-org synapse: from 1.113.0rc1, < 1.120.1

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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