Python-Multipart przed wersją 0.0.30 vulnerabilities

In the Python-Multipart library before version 0.0.31, the parse_form() function did not validate the Content-Length header before using it to bound its chunked read of the request body. A negative Content-Length turned the bounded read into a read-until-EOF, so the entire body was loaded into memory in a single read instead of in fixed-size chunks.

The vulnerability in Python-Multipart before version 0.0.30 causes quadratic computational complexity when parsing application/x-www-form-urlencoded bodies using semicolons as separators. An attacker can send a small crafted request with many semicolon-separated fields, leading to high CPU usage and potential resource exhaustion.

Python-Multipart before version 0.0.30 incorrectly treated the semicolon (;) as a field separator in application/x-www-form-urlencoded bodies, while the WHATWG standard and modern browsers only recognize the & character. This parsing differential allows an attacker to smuggle extra form fields past an upstream body inspecting component.

The vulnerability in Python-Multipart before version 0.0.30 is that the parse_options_header function decodes Content-Disposition and Content-Type headers according to RFC 2231/5987, allowing the use of extended parameter syntax (e.g., filename*=charset'lang'value). An attacker can exploit this difference in header interpretation between components (e.g., WAF, proxy) and the backend to smuggle a different field name or filename, bypassing security inspection.