What’s Vulnerable › Vulnerabilities

CVE-2026-40347: Python-Multipart affected by Denial of Service via large multipart preamble or epilogue data

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-18 · updated 2026-10-26
• Weakness: CWE-400

Description

Python-Multipart is a streaming multipart parser for Python. Versions prior to 0.0.26 have a denial of service vulnerability when parsing crafted `multipart/form-data` requests with large preamble or epilogue sections. Upgrade to version 0.0.26 or later, which skips ahead to the next boundary candidate when processing leading CR/LF data and immediately discards epilogue data after the closing boundary.

Affected products

• Kludex python-multipart: before 0.0.26 — fixed in 0.0.26

How to fix

Upgrade to a fixed version: Kludex python-multipart 0.0.26. Check the vendor advisory for mitigations.

References

• https://github.com/Kludex/python-multipart/releases/tag/0.0.26
• https://github.com/Kludex/python-multipart/security/advisories/GHSA-mj87-hwqh-73pj

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