CVE-2026-53538

Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, QuerystringParser treated ; as a field separator in application/x-www-form-urlencoded bodies, in addition to &. The WHATWG URL standard, modern browsers, and Python's urllib.parse (since the CVE-2021-23336 fix) treat only & as a separator. This creates a parser differential: the same bytes are tokenized into different fields than a WHATWG compliant intermediary would produce, allowing an attacker to smuggle extra form fields past an upstream body inspecting component. This vulnerability is fixed in 0.0.30.

CVSS v3 3.7 LOW

3.7^/10

CVSS v3 : LOW

Vector :

Exploitability : 2.2 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact LOW

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/Kludex/python-multipart/security/advisories/GHSA-6jv3-5f52-599m	Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:fastapiexpert:python-multipart:*:*:*:*:*:python:*:*

History

26 Jun 2026, 19:52

Type	Values Removed	Values Added
References	~~() https://github.com/Kludex/python-multipart/security/advisories/GHSA-6jv3-5f52-599m -~~	() https://github.com/Kludex/python-multipart/security/advisories/GHSA-6jv3-5f52-599m - Vendor Advisory
First Time		Fastapiexpert python-multipart Fastapiexpert
CPE		cpe:2.3:a:fastapiexpert:python-multipart::::::python::*

22 Jun 2026, 18:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-06-22 18:16

Updated : 2026-06-26 19:52

NVD link : CVE-2026-53538

Mitre link : CVE-2026-53538

CVE.ORG link : CVE-2026-53538

JSON object : View

Products Affected

fastapiexpert

python-multipart

CWE

CWE-436

Interpretation Conflict

CWE-444

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

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