CVE-2026-53539: Python-Multipart is a streaming multipart parser for Python

This month

HIGH 7.5REMOTEUPGRADE

CVE-2026-53539 is a high-severity flaw (CVSS 7.5) 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. Prior to 0.0.30, when parsing application/x-www-form-urlencoded bodies, QuerystringParser located the field separator with a two step lookup: it first scanned the entire remaining buffer for &, and only when no & existed anywhere ahead did it fall back to scanning for ;. For a body that uses ; as the separator and contains no &, every field iteration performed a full failed & scan over

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 60%)
CISA exploited list	No
Weakness	CWE-400, CWE-407
Published	2026-06-22
Last modified	2026-10-25

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

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-22 18:16 UTCPublished CVE record published
2026-10-25 23:10 UTCUpdated Record last modified

fastapiexpert python-multipart UPGRADE

Affected: < 0.0.30

Fixed in: 0.0.30

Safe to downgrade to: no unaffected older release

1. Check installed version

pip show python-multipart

2. UPGRADE to 0.0.30

pip install --upgrade "python-multipart>=0.0.30"

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-2026-53539?

python-multipart: upgrade to 0.0.30. Exact commands for each OS are on this page.

Is CVE-2026-53539 being exploited?

CVE-2026-53539 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-2026-53539 affect?

CVE-2026-53539 affects python-multipart. Severity is high (CVSS 7.5). Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, when parsing application/x-www-form-urlencoded bodies, QuerystringParser located the field separator with a two step lookup: it first scanned the entire remaining

How urgent is CVE-2026-53539?

Priority 41/100. High severity; Remotely exploitable, no login, no user action

Software pages

Python vulnerabilities

Related CVEs

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

← Back to latest CVEs