# CVE-2026-53540: Kludex Python-Multipart denial of service via negative Content-Length

Source: https://junglewise.ai/threats/cve-2026-53540-kludex-python-multipart-denial-of-service-via-negative-content  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-22. Updated: 2026-06-22  
License: CC BY 4.0 with a link back

CVE-2026-53540 · Severity: low · CVSS 3.7 · Published 2026-06-22

Python-Multipart is a library used by web applications to process data sent through web forms. A flaw in how it handles specific web headers could allow an attacker to force the application to load an entire large file into memory at once instead of processing it in small pieces. This could lead to increased memory usage and potentially slow down or crash the service if multiple such requests are sent simultaneously.

Technologies: [python-multipart (PyPI)](https://junglewise.ai/threats/technologies/python-multipart). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-53540 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-53540 being exploited in the wild.

**How severe is CVE-2026-53540?** Low severity, with a CVSS score of 3.7, published 22 June 2026.

**Which products and versions are affected?** python-multipart (PyPI) < 0.0.31, ECOSYSTEM:introduced=0,fixed=0.0.31.

**Is there a fix for CVE-2026-53540?** Yes. python-multipart (PyPI): upgrade to 0.0.31 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-53540 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-53540?** Check whether you run python-multipart (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- python-multipart (PyPI): upgrade to 0.0.31 or later

  ```sh
  pip install "python-multipart>=0.0.31"
  ```


## Technical details

A vulnerability exists in the parse_form() function of python-multipart where the Content-Length header is not validated for negative values. When a negative value is provided, the internal logic min(content_length - bytes_read, chunk_size) results in a negative value being passed to the stream's read() method, which triggers a read-until-EOF behavior. This causes the entire request body to be buffered into memory in a single operation rather than being processed in fixed-size chunks. Exploitation requires the application to call parse_form() directly using raw, un-normalized attacker-controlled headers. The issue is resolved in version 0.0.31.

## Affected products

- Kludex python-multipart < 0.0.31

## Identifiers

- CVE-2026-53540
- GHSA-v9pg-7xvm-68hf
- PYSEC-2026-3040

## Timeline

- 2026-06-04: advisory: GitHub advisory published by maintainer
- 2026-06-22: disclosed: CVE published to NVD
- 2026-06-22: patched: Fix released in version 0.0.31

## References

- [https://github.com/Kludex/python-multipart/security/advisories/GHSA-v9pg-7xvm-68hf](https://github.com/Kludex/python-multipart/security/advisories/GHSA-v9pg-7xvm-68hf)

## Related threats

- [PYSEC-2026-1851 - Denial of service (DoS) via deformation `multipart/form-data` boundary](https://junglewise.ai/threats/cve-2024-53981-denial-of-service-dos-via-deformation-multipart-form-data)
- [PYSEC-2026-1850 - python-multipart vulnerable to Content-Type Header ReDoS](https://junglewise.ai/threats/cve-2024-24762-python-multipart-content-type-header-redos)
- [Kludex Python-Multipart denial of service in QuerystringParser](https://junglewise.ai/threats/cve-2026-53539-kludex-python-multipart-denial-of-service-in-querystringparser)
- [Kludex Python-Multipart parameter smuggling via semicolon separator](https://junglewise.ai/threats/cve-2026-53538-kludex-python-multipart-parameter-smuggling-via-semicolon)
- [Kludex Python-Multipart parameter smuggling in Content-Disposition header](https://junglewise.ai/threats/cve-2026-53537-kludex-python-multipart-parameter-smuggling-in-content)