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CVE-2026-40347

MEDIUMCVSS 5.3/10EPSS 0.35%

Last modified

CVE-2026-40347 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. 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. EPSS estimates a 0.35% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1
5.3/10

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

EPSS Probability
0.35%

27.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
FastapiexpertPython-Multipart< 0.0.26

References

Timeline

Published
Last Modified
Status
Analyzed

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.
How severe is CVE-2026-40347?
CVE-2026-40347 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 0.35% probability of exploitation in the next 30 days.
How do I fix CVE-2026-40347?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-40347?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST