Summary
matrix-media-repo (MMR) allows denial of service/high operating costs through unauthenticated downloads
Workarounds
Operators may wish to lower the maximum file size they allow and implement harsh rate limits, though this can still lead to a large amount of data to be downloaded.
References
Impact
MMR before version 1.3.5 is vulnerable to unbounded disk consumption, where an unauthenticated adversary can induce it to download and cache large amounts of remote media files.
MMR's typical operating environment uses S3-like storage as a backend, with file-backed store as an alternative option. Instances using a file-backed store or those which self-host an S3 storage system are therefore vulnerable to a disk fill attack. Once the disk is full, authenticated users will be unable to upload new media, resulting in denial of service.
For instances configured to use a cloud-based S3 storage option, this could result in high service fees instead of a denial of service.
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-2024-36403 has a CVSS score of 5.3 (Medium). 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 (1.3.5); 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.
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MMR 1.3.5 introduces a new default-on "leaky bucket" rate limit 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.
Operators should note that the leaky bucket implementation introduced in MMR 1.3.5 requires the IP address associated with the request to be forwarded, to avoid mistakenly applying the rate limit to the reverse proxy instead. To avoid this issue, the reverse proxy should populate the X-Forwarded-For header when sending the request to MMR.
Frequently Asked Questions
- What is CVE-2024-36403? CVE-2024-36403 is a medium-severity allocation of resources without limits or throttling vulnerability in github.com/t2bot/matrix-media-repo (go), affecting versions < 1.3.5. It is fixed in 1.3.5. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
- How severe is CVE-2024-36403? CVE-2024-36403 has a CVSS score of 5.3 (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 github.com/t2bot/matrix-media-repo are affected by CVE-2024-36403? github.com/t2bot/matrix-media-repo (go) versions < 1.3.5 is affected.
- Is there a fix for CVE-2024-36403? Yes. CVE-2024-36403 is fixed in 1.3.5. Upgrade to this version or later.
- Is CVE-2024-36403 exploitable, and should I be worried? Whether CVE-2024-36403 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-2024-36403 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-2024-36403? Upgrade
github.com/t2bot/matrix-media-repoto 1.3.5 or later.