CVE-2024-37302

Synapse denial of service through media disk space consumption

Workarounds

Synapse deployments can currently decrease the maximum file size allowed, as well as increase request rate limits. However, this does not as effectively address the issue as a dedicated rate limit on remote media downloads.

Server operators may also wish to consider putting media on a dedicated disk or volume, reducing the impact of a disk fill condition.

References

• https://en.wikipedia.org/wiki/Leaky_bucket#As_a_meter

For more information

If you have any questions or comments about this advisory, please email us at security at element.io.

Synapse versions before 1.106 are vulnerable to a disk fill attack, where an unauthenticated adversary can induce Synapse to download and cache large amounts of remote media. The default rate limit strategy is insufficient to mitigate this. This can lead to a denial of service, ranging from further media uploads/downloads failing to completely unavailability of the Synapse process, depending on how Synapse was deployed.

The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.

CVE-2024-37302 has a CVSS score of 7.5 (High). The vector is network-reachable, no 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 (1.106); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Synapse 1.106 introduces a new "leaky bucket" rate limit on remote media downloads to reduce the amount of data a user can request at a time. This does not fully address the issue, but does limit an unauthenticated user's ability to request large amounts of data to be cached.

1. What is CVE-2024-37302? CVE-2024-37302 is a high-severity allocation of resources without limits or throttling vulnerability in matrix-synapse (pip), affecting versions < 1.106. It is fixed in 1.106. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
2. How severe is CVE-2024-37302? CVE-2024-37302 has a CVSS score of 7.5 (High). 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.
3. Which versions of matrix-synapse are affected by CVE-2024-37302? matrix-synapse (pip) versions < 1.106 is affected.
4. Is there a fix for CVE-2024-37302? Yes. CVE-2024-37302 is fixed in 1.106. Upgrade to this version or later.
5. Is CVE-2024-37302 exploitable, and should I be worried? Whether CVE-2024-37302 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
6. What actually determines whether CVE-2024-37302 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.
7. How do I fix CVE-2024-37302? Upgrade matrix-synapse to 1.106 or later.

Other vulnerabilities in matrix-synapse