CVE-2026-53539
Python-Multipart: Quadratic-time querystring parsing with semicolon separators causes CPU denial of service
Description
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.
INFO
Published Date :
June 22, 2026, 6:16 p.m.
Last Modified :
June 26, 2026, 7:50 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | MITRE-CVE | ||||
| CVSS 3.1 | HIGH | [email protected] |
Solution
- Update Python-Multipart to 0.0.30 or later.
- Ensure proper input validation for form data.
- Monitor system performance for resource exhaustion.
Public PoC/Exploit Available at Github
CVE-2026-53539 has a 5 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-53539.
| URL | Resource |
|---|---|
| https://github.com/Kludex/python-multipart/security/advisories/GHSA-5rvq-cxj2-64vf | Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-53539 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-53539
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
None
Dockerfile Python HTML Mako Shell
Upload a PDF, DOCX, or TXT document and get back a validated extraction: summary, entities, key dates, key terms, and action items -- stored in SQLite and served over a REST API, with a Streamlit UI on top.
Python Dockerfile
NotebookLM MCP CLI - Access NotebookLM via Claude with security fixes and FastMCP 1.0 compatibility
Python
MVidarr - The Music Video Management System
HTML Python Shell JavaScript CSS TypeScript Batchfile Dockerfile Mako Go Template
All Public RunWhen Helm Charts - Managed by terraform
Shell Dockerfile Go Template
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-53539 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-53539 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Jun. 26, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:fastapiexpert:python-multipart:*:*:*:*:*:python:*:* versions up to (excluding) 0.0.30 Added Reference Type GitHub, Inc.: https://github.com/Kludex/python-multipart/security/advisories/GHSA-5rvq-cxj2-64vf Types: Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 23, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-53539', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-06-23T14:05:50.901666Z'} -
New CVE Received by [email protected]
Jun. 22, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'Kludex', 'product': 'python-multipart', 'versions': [{'status': 'affected', 'version': '< 0.0.30'}]}] Added Description 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Added CWE CWE-407 Added CWE CWE-400 Added Reference https://github.com/Kludex/python-multipart/security/advisories/GHSA-5rvq-cxj2-64vf