Goal Reached Thanks to every supporter — we hit 100%!

Goal: 1000 CNY · Raised: 1359 CNY

100%
Buy Us a Coffee

CVE-2026-53538— Python-Multipart: Semicolon treated as querystring field separator enables parameter smuggling

Quick assessment

Affected
Kludex python-multipart
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Kludex python-multipart是Kludex的开源Web中间件流式解析库。 Kludex python-multipart 0.0.30之前版本存在安全漏洞，该漏洞源于QuerystringParser将;和&均作为application/x-www-form-urlencoded正文中的字段分隔符处理，而WHATWG URL标准、现代浏览器及Python的urllib.parse仅将&视为分隔符，导致解析差异，允许攻击者绕过上游正文检查组件夹带额外表单字段。

CVSS 3.7 · Low EPSS 0.26% · P16

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
Kludex python-multipart < 0.0.30 affected
Get alerts for future matching vulnerabilities Log in to subscribe

I. Basic Information for CVE-2026-53538

Vulnerability Information
Have questions about the vulnerability? See if Shenlong's analysis helps!
View Shenlong Deep Dive ↗

Although we use advanced large model technology, its output may still contain inaccurate or outdated information.Shenlong tries to ensure data accuracy, but please verify and judge based on the actual situation.

Vulnerability Title
Python-Multipart: Semicolon treated as querystring field separator enables parameter smuggling
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
解释冲突
Source: CVE Program / CVE List V5
Vulnerability Title
Kludex python-multipart 处理逻辑错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Kludex python-multipart是Kludex的开源Web中间件流式解析库。 Kludex python-multipart 0.0.30之前版本存在安全漏洞，该漏洞源于QuerystringParser将;和&均作为application/x-www-form-urlencoded正文中的字段分隔符处理，而WHATWG URL标准、现代浏览器及Python的urllib.parse仅将&视为分隔符，导致解析差异，允许攻击者绕过上游正文检查组件夹带额外表单字段。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Kludex python-multipart < 0.0.30 -

II. Public POCs for CVE-2026-53538

# POC Description Source Link Shenlong Link
AI-Generated POC Premium

No public POC found.

Login to generate AI POC

III. Intelligence Information for CVE-2026-53538

请登录查看更多情报信息。

Vendor Advisories for CVE-2026-53538 (1)

Same Patch Batch · Kludex · 2026-06-22 · 6 CVEs total

CVE-2026-53539 7.5 HIGH Python-Multipart: Quadratic-time querystring parsing with semicolon separators causes CPU
CVE-2026-54283 7.5 HIGH Starlette: request.form() limits silently ignored for application/x-www-form-urlencoded en
CVE-2026-53537 3.7 LOW Python-Multipart: Content-Disposition parameter smuggling via RFC 2231/5987 extended param
CVE-2026-53540 3.7 LOW Python-Multipart: Negative Content-Length in parse_form buffers the entire body in memory
CVE-2026-54282 3.7 LOW Starlette: Unvalidated request path concatenated into authority poisons request.url.hostna

IV. Related Vulnerabilities

Same product: python-multipart
Same vendor: Kludex
Same weakness: CWE-436

V. Comments for CVE-2026-53538

No comments yet

Leave a comment