CVE-2026-40347

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.

CVSS v3.1 Score

5.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS — Exploit Prediction

0.0002

Probability of exploitation

0.06%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-400 Uncontrolled Resource Consumption

CWE-834 CWE-834

Affected Products

Vendor	Product	Versions
fastapiexpert	python-multipart	< 0.0.26

References

Advisories & Patches

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

Other References

https://github.com/Kludex/python-multipart/releases/tag/0.0.26

Frequently Asked Questions

What is CVE-2026-40347? +

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. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-40347? +

CVE-2026-40347 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0002, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-40347? +

CVE-2026-40347 affects products from fastapiexpert, specifically: python-multipart. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-40347? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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