Summary
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.
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.
CVE-2024-53867 has a CVSS score of 4.3 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.120.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Synapse version 1.120.1 fixes the problem.
Frequently Asked Questions
- What is CVE-2024-53867? CVE-2024-53867 is a medium-severity security vulnerability in matrix-synapse (pip), affecting versions >= 1.113.0rc1, < 1.120.1. It is fixed in 1.120.1.
- How severe is CVE-2024-53867? CVE-2024-53867 has a CVSS score of 4.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of matrix-synapse are affected by CVE-2024-53867? matrix-synapse (pip) versions >= 1.113.0rc1, < 1.120.1 is affected.
- Is there a fix for CVE-2024-53867? Yes. CVE-2024-53867 is fixed in 1.120.1. Upgrade to this version or later.
- Is CVE-2024-53867 exploitable, and should I be worried? Whether CVE-2024-53867 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2024-53867 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2024-53867? Upgrade
matrix-synapseto 1.120.1 or later.