CVE-2026-53538

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Source
https://cve.org/CVERecord?id=CVE-2026-53538
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53538.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-53538
Aliases
Downstream
Related
Published
2026-06-22T16:56:32.628Z
Modified
2026-07-08T08:11:31.034434351Z
Severity
  • 3.7 (Low) CVSS_V3 - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N CVSS Calculator
Summary
Python-Multipart: Semicolon treated as querystring field separator enables parameter smuggling
Details

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.

Database specific 
{
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53538.json",
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
        "CWE-436",
        "CWE-444"
    ]
}
References

Affected packages

Git / github.com/kludex/python-multipart

Affected ranges

Type
GIT
Repo
https://github.com/kludex/python-multipart
Events
Introduced
0 Unknown introduced commit / All previous commits are affected
Fixed
9d3ead568a259f222cff6425262ff63e88d930d4
Database specific 
{
    "cpe": "cpe:2.3:a:fastapiexpert:python-multipart:*:*:*:*:*:python:*:*",
    "extracted_events": [
        {
            "introduced": "0"
        },
        {
            "fixed": "0.0.30"
        }
    ],
    "source": [
        "AFFECTED_FIELD",
        "CPE_RANGE"
    ]
}

Affected versions

0.*
0.0.10
0.0.11
0.0.12
0.0.13
0.0.14
0.0.15
0.0.16
0.0.17
0.0.18
0.0.19
0.0.2
0.0.20
0.0.21
0.0.22
0.0.23
0.0.24
0.0.25
0.0.26
0.0.27
0.0.28
0.0.29
0.0.4
0.0.5
0.0.6
0.0.7
0.0.8
0.0.9

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53538.json"