CVE-2023-30798

Workarounds

Applications that don't install python-multipart or that don't use form fields are safe.

In older versions, it's also possible to instead of calling request.form() call request.stream() and parse the form data in internal code.

In most cases, the best solution is to upgrade the Starlette version.

References

This was reported in private by @das7pad via internal email. He also coordinated the fix across multiple frameworks and parsers.

The details about how multipart/form-data is structured and parsed are in the RFC 7578.

The MultipartParser using the package python-multipart accepts an unlimited number of multipart parts (form fields or files).

Processing too many parts results in high CPU usage and high memory usage, eventually leading to an OOM process kill.

This can be triggered by sending too many small form fields with no content, or too many empty files.

For this to take effect application code has to:

• Have python-multipart installed and
• call request.form()
  • or via another framework like FastAPI, using form field parameters or UploadFile parameters, which in turn calls request.form().

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2023-30798 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 (0.25.0); upgrading removes the vulnerable code path.

Kodem intelligence

The vulnerability is solved in Starlette 0.25.0 by making the maximum fields and files customizable and with a sensible default (1000).

Applications will be secure by just upgrading their Starlette version to 0.25.0 (or FastAPI to 0.92.0).

If application code needs to customize the new max field and file number, there are new request.form() parameters (with the default values):

• max_files=1000
• max_fields=1000

1. What is CVE-2023-30798? CVE-2023-30798 is a high-severity uncontrolled resource consumption vulnerability in starlette (pip), affecting versions < 0.25.0. It is fixed in 0.25.0. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2023-30798? CVE-2023-30798 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 starlette are affected by CVE-2023-30798? starlette (pip) versions < 0.25.0 is affected.
4. Is there a fix for CVE-2023-30798? Yes. CVE-2023-30798 is fixed in 0.25.0. Upgrade to this version or later.
5. Is CVE-2023-30798 exploitable, and should I be worried? Whether CVE-2023-30798 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-2023-30798 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-2023-30798? Upgrade starlette to 0.25.0 or later.