Kludex python-multipart up to 0.0.29 on Python resource consumption

Summaryinfo

A vulnerability was found in Kludex python-multipart up to 0.0.29 on Python. It has been classified as problematic. The affected element is an unknown function. Performing a manipulation results in resource consumption. This vulnerability is identified as CVE-2026-53539. The attack can be initiated remotely. There is not any exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in Kludex python-multipart up to 0.0.29 on Python. It has been classified as problematic. This affects an unknown code block. The manipulation with an unknown input leads to a resource consumption vulnerability. CWE is classifying the issue as CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. This is going to have an impact on availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-53539 since 06/09/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 0.0.30 eliminates this vulnerability.

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Productinfo

Type

• Programming Language Software

Vendor

• Kludex

Name

• python-multipart

Version

• 0.0.1
• 0.0.2
• 0.0.3
• 0.0.4
• 0.0.5
• 0.0.6
• 0.0.7
• 0.0.8
• 0.0.9
• 0.0.10
• 0.0.11
• 0.0.12
• 0.0.13
• 0.0.14
• 0.0.15
• 0.0.16
• 0.0.17
• 0.0.18
• 0.0.19
• 0.0.20
• 0.0.21
• 0.0.22
• 0.0.23
• 0.0.24
• 0.0.25
• 0.0.26
• 0.0.27
• 0.0.28
• 0.0.29

Website

• Product: https://github.com/Kludex/python-multipart/

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