CVE-2023-25577

Unlimited multipart form data parsing in Werkzeug prior to 2.2.3 can lead to denial of service

• CVSS 7.5
• CWE-770 Allocation of Resources Without Limits or Throttling
• Resource Management
• Remote

Werkzeug is a comprehensive WSGI web application library. Prior to version 2.2.3, Werkzeug's multipart form data parser will parse an unlimited number of parts, including file parts. Parts can be a small amount of bytes, but each requires CPU time to parse and may use more memory as Python data. If a request can be made to an endpoint that accesses `request.data`, `request.form`, `request.files`, or `request.get_data(parse_form_data=False)`, it can cause unexpectedly high resource usage. This allows an attacker to cause a denial of service by sending crafted multipart data to an endpoint that will parse it. The amount of CPU time required can block worker processes from handling legitimate requests. The amount of RAM required can trigger an out of memory kill of the process. Unlimited file parts can use up memory and file handles. If many concurrent requests are sent continuously, this can exhaust or kill all available workers. Version 2.2.3 contains a patch for this issue.

CVE

CVE-2023-25577

CWE

CWE-770 Allocation of Resources Without Limits or Throttling

CVSS base score

7.5

Published

2023-02-14

OWASP

A08 Software and Data Integrity Failures

Orthogonal defect classification

Function

Code defect classification

Incorrect Functionality

Category

Resource Management

Subcategory

Resource Exhaustion

Accessibility scope

Remote

Impact

Denial of Service (DoS)

Fixed by upgrading

Yes

Solution

Update Werkzeug to version 2.2.3 or higher.

from flask import Flask, request

app = Flask(__name__)

@app.route('/upload', methods=['POST'])
def upload_file():
    for file in request.files.getlist('files'):
        pass

    return 'Files uploaded successfully', 200

if __name__ == '__main__':
    app.run()

from flask import Flask, request, abort

app = Flask(__name__)

MAX_FILE_PARTS = 10

@app.route('/upload', methods=['POST'])
def upload_file():
    if len(request.files) > MAX_FILE_PARTS:
        abort(413)

    for file in request.files.getlist('files'):
        pass

    return 'Files uploaded successfully', 200

if __name__ == '__main__':
    app.run()

@misc{vaitp:cve202325577,
  title        = {{Unlimited multipart form data parsing in Werkzeug prior to 2.2.3 can lead to denial of service}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2023},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2023-25577},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2023-25577/}}
}