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CVE-2026-53537— Python-Multipart: Content-Disposition parameter smuggling via RFC 2231/5987 extended parameters

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parse_options_header解析Content-Disposition和Content-Type标头时应用RFC 2231/5987解码，攻击者可利用解码差异将不同的字段名或文件名绕过上游检查器走私到后端。

CVSS 3.7 · Low EPSS 0.29% · P20

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
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I. Basic Information for CVE-2026-53537

Vulnerability Information
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Vulnerability Title
Python-Multipart: Content-Disposition parameter smuggling via RFC 2231/5987 extended parameters
Source: CVE Program / CVE List V5
Vulnerability Description
Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, parse_options_header parsed Content-Disposition (and Content-Type) headers with email.message.Message, which transparently applies RFC 2231/5987 decoding. The extended parameter syntax (filename*=charset'lang'value, name*=..., and the filename*0/filename*1 continuation form) is decoded and surfaced under the bare filename/name key, and overrides the plain parameter when both are present. RFC 7578 §4.2 explicitly forbids the filename* form in multipart/form-data. Components that follow RFC 7578, or that do not implement RFC 2231/5987 decoding for multipart/form-data (WAFs, proxies, gateways), may interpret such a header differently. An attacker can exploit that difference to smuggle a different field name or filename past an upstream inspector to the backend. 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
输入验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Kludex python-multipart 输入验证错误漏洞
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parse_options_header解析Content-Disposition和Content-Type标头时应用RFC 2231/5987解码，攻击者可利用解码差异将不同的字段名或文件名绕过上游检查器走私到后端。
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-2026-53537

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III. Intelligence Information for CVE-2026-53537

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Vendor Advisories for CVE-2026-53537 (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-2026-53540 3.7 LOW Python-Multipart: Negative Content-Length in parse_form buffers the entire body in memory
CVE-2026-53538 3.7 LOW Python-Multipart: Semicolon treated as querystring field separator enables parameter smugg
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-20

V. Comments for CVE-2026-53537

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