Vulnerabilidad · Publicado 22/06/2026 · Actualizado 01/08/2026
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 fi…
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.
Score: 7.5/10 — Severidad: HIGH — Estado NIST: Analyzed
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Python-multipart — Fastapiexpert
CWE-400, CWE-407
Publicado en NIST NVD.