CVE-2024-53981

When parsing form data, python-multipart skips line breaks (CR \r or LF \n) in front of the first boundary and any tailing bytes after the last boundary. This happens one byte at a time and emits a log event each time, which may cause excessive logging for certain inputs.

An attacker could abuse this by sending a malicious request with lots of data before the first or after the last boundary, causing high CPU load and stalling the processing thread for a significant amount of time. In case of ASGI application, this could stall the event loop and prevent other requests from being processed, resulting in a denial of service (DoS).

Original Report

This security issue was reported by:

• GitHub security advisory in Starlette on October 30 by @Startr4ck
• Email to python-multipart maintainer on October 3 by @mnqazi

Applications that use python-multipart to parse form data (or use frameworks that do so) are affected.

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-2024-53981 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 (0.0.18); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2024-53981? CVE-2024-53981 is a high-severity allocation of resources without limits or throttling vulnerability in python-multipart (pip), affecting versions < 0.0.18. It is fixed in 0.0.18. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
2. How severe is CVE-2024-53981? CVE-2024-53981 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 python-multipart are affected by CVE-2024-53981? python-multipart (pip) versions < 0.0.18 is affected.
4. Is there a fix for CVE-2024-53981? Yes. CVE-2024-53981 is fixed in 0.0.18. Upgrade to this version or later.
5. Is CVE-2024-53981 exploitable, and should I be worried? Whether CVE-2024-53981 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-2024-53981 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-2024-53981? Upgrade python-multipart to 0.0.18 or later.