CVE-2026-53537

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

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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.

CVSS 3.7 · Faible · EPSS 0,3% · Correctif disponible

Publication

2026-06-22T16:57:21.496Z

Mise à jour

2026-06-23T16:08:07.690Z

Pile logicielle: system · python

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