CVE-2026-53539
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk18th percentile — higher than 18% of all known CVEs
Summary
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.
Risk Assessment
The risk is a potential Denial of Service (DoS) attack where a few concurrent requests can exhaust worker processes, causing service unavailability.
Recommendation
Immediately upgrade Python-Multipart to version 0.0.30 or later, which contains the fix for this vulnerability.
Original NVD description (English source)
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.