Denial of service (DoS) via deformation `multipart/form-data` boundaryGHSA-59g5-xgcq-4qw3
HIGHFix: Kludex/python-multipart@c4fe4d3GHSA-59g5-xgcq-4qw3 is a high-severity (CVSS 7.5) CWE-770 vulnerability in python-multipart. A fix is available for python-multipart — see the affected versions and patch details below.
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-59g5-xgcq-4qw3.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
python-multipartReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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).
Impact
Applications that use python-multipart to parse form data (or use frameworks that do so) are affected.
Original Report
This security issue was reported by:
- GitHub security advisory in Starlette on October 30 by @Startr4ck
- Email to
python-multipartmaintainer on October 3 by @mnqazi
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | python-multipart | all versions | 0.0.18pip install --upgrade 'python-multipart==0.0.18' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for python-multipart, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update python-multipart to 0.0.18 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-59g5-xgcq-4qw3 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Frequently Asked Questions
Is GHSA-59g5-xgcq-4qw3 in your dependencies?
Find it across PyPI, including transitive dependencies.