CVE-2026-40347: Python-Multipart is a streaming multipart parser for Python

Routine

MEDIUM 5.3REMOTEUPGRADE

CVE-2026-40347 is a medium-severity flaw (CVSS 5.3) affecting python-multipart. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 72%)
CISA exploited list	No
Weakness	CWE-400, CWE-834
Published	2026-04-18
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: fastapiexpert

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-18 00:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

fastapiexpert python-multipart UPGRADE

Affected: < 0.0.26

Fixed in: 0.0.26

Safe to downgrade to: no unaffected older release

1. Check installed version

pip show python-multipart

2. UPGRADE to 0.0.26

pip install --upgrade "python-multipart>=0.0.26"

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-40347?

python-multipart: upgrade to 0.0.26. Exact commands for each OS are on this page.

Is CVE-2026-40347 being exploited?

CVE-2026-40347 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-40347 affect?

CVE-2026-40347 affects python-multipart. Severity is medium (CVSS 5.3). 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.

How urgent is CVE-2026-40347?

Priority 31/100. Remotely exploitable, no login, no user action

Software pages

Python vulnerabilities

Related CVEs

CVE-2026-53539 HIGH 7.5 UPGRADE Python-Multipart is a streaming multipart parser for Python
CVE-2026-53540 LOW 3.7 UPGRADE Python-Multipart is a streaming multipart parser for Python
CVE-2026-53537 LOW 3.7 UPGRADE Python-Multipart is a streaming multipart parser for Python
CVE-2026-53538 LOW 3.7 UPGRADE Python-Multipart is a streaming multipart parser for Python

References

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