Summary
Synapse allows unsupported content types to lead to memory exhaustion
Workarounds
Limiting request sizes or blocking the multipart/form-data content type before the requests reach Synapse, for example in a reverse proxy, alleviates the issue. Another approach that mitigates the attack is to use a low max_upload_size in Synapse.
References
- https://github.com/twisted/twisted/issues/4688#issuecomment-1167705518
- https://github.com/twisted/twisted/issues/4688#issuecomment-2385711609
For more information
If you have any questions or comments about this advisory, please email us at security at element.io.
Impact
In Synapse before 1.120.1, multipart/form-data requests can in certain configurations transiently increase memory consumption beyond expected levels while processing the request, which can be used to amplify denial of service attacks.
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.
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.
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Synapse 1.120.1 resolves the issue by denying requests with unsupported multipart/form-data content type.
Frequently Asked Questions
- What is CVE-2024-52805? CVE-2024-52805 is a high-severity allocation of resources without limits or throttling vulnerability in matrix-synapse (pip), affecting versions < 1.120.1. It is fixed in 1.120.1. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
- Which versions of matrix-synapse are affected by CVE-2024-52805? matrix-synapse (pip) versions < 1.120.1 is affected.
- Is there a fix for CVE-2024-52805? Yes. CVE-2024-52805 is fixed in 1.120.1. Upgrade to this version or later.
- Is CVE-2024-52805 exploitable, and should I be worried? Whether CVE-2024-52805 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-2024-52805 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-2024-52805? Upgrade
matrix-synapseto 1.120.1 or later.