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CVE-2021-32838 targets Flask-RESTX, an API extension that Freshermeat integrated into version 0.8.0 to handle request parsing and Swagger documentation.
The vulnerability stems from a regular expression flaw in the email parsing or field validation component of Flask-RESTX.
When an application utilizes vulnerable versions of Flask-RESTX for parsing incoming web payloads, malicious users can supply specifically crafted input strings.
These malicious strings trigger catastrophic backtracking within the regular expression engine utilized by the parsing module.
As the regex engine struggles to match the pathological input against complex patterns, CPU utilization spikes to maximum capacity.
This computational bottleneck blocks event loops or worker threads, halting the processing of legitimate user requests across the instance.
In a release-tracking platform like Freshermeat, CVE workers and REST endpoints become entirely unresponsive during an active attack.
The underlying mechanism exploits linear regex evaluations turning into exponential time complexity under specific malicious payloads.
Because Flask-RESTX handles automated API request validation globally across endpoints, a single malicious request can freeze worker processes.
Async workers trying to fetch CVE feeds or parse external repository releases also experience cascading lockups due to thread exhaustion.
Developers integrating third-party dependencies must ensure that underlying parsing libraries are updated past vulnerable thresholds.
The transition to Flask-RESTX in Freshermeat version 0.8.0 initially introduced this exposure until dependency pinning and updates were enforced.
Mitigating this issue requires upgrading the package to version 0.5.1 or later, where the vulnerable regular expression was safely refactored.
Security monitoring tools integrated into platforms like Freshermeat help identify vulnerable library versions before exploitation occurs.
Maintaining up-to-date back-end and front-end dependencies is a core pillar of preventing supply chain vulnerabilities in modern Python apps.
DailyCVE Form:
Platform: Flask RESTX integration
Version: Prior version zero
Vulnerability : Regular expression denial
Severity : Medium risk level
date: September 2021
Prediction: Patch already released
What Undercode Say:
Analytics of Freshermeat CVE tracking and Flask-RESTX integration show significant backend improvements across releases 0.8.0 and 0.8.1. Migrating commands to the internal Flask CLI and updating dependencies resolved concurrency bottlenecks.
Bash commands and codes:
pip install --upgrade flask-restx python -m freshermeat db upgrade pytest tests/test_api.py
Exploit: (Educational Purposes!)
import requests
url = "http://localhost:5000/api/"
payload = "a" 10000 + "!"
response = requests.get(url, params={"input": payload})
print(response.status_code)
Protection: from this CVE
Upgrade Flask-RESTX to version 0.5.1 or later where the regular expression backtracking issue has been patched. Ensure all backend requirements in requirements.txt or pyproject.toml are regularly audited using dependency scanners.
Impact:
Exploitation leads to high CPU consumption, application freeze, and denial of service for administrative dashboards, CVE workers, and REST API endpoints.
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Sources:
Reported By: github.com
Extra Source Hub:
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