CVE-2026-53539— Python-Multipart: Quadratic-time querystring parsing with semicolon separators causes CPU denial of service

Python-Multipart: Quadratic-time querystring parsing with semicolon separators causes CPU denial of service

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 the entire remaining buffer before locating the nearby ;. With N semicolon separated fields in a chunk of size B, this yields O(B^2) byte comparisons per chunk. An attacker can submit a small crafted body of the form a;a;a;... and cause the parser to spend seconds of CPU per request. A handful of concurrent requests can exhaust worker processes. This vulnerability is fixed in 0.0.30.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

未加控制的资源消耗(资源穷尽)

Kludex python-multipart 资源管理错误漏洞

Kludex python-multipart是Kludex的开源Web中间件流式解析库。 python-multipart 0.0.30之前版本存在资源管理错误漏洞，该漏洞源于解析application/x-www-form-urlencoded主体时，QuerystringParser定位字段分隔符的扫描方式不当，可能导致CPU消耗过高，攻击者可通过特制请求造成拒绝服务。以下版本受到影响：0.0.30之前版本。

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