CVE-2024-37891

Improper handling of `Proxy-Authorization` header in urllib3 may expose users.

• CVSS 6.5
• CWE-669
• Authentication, Authorization, and Session Management
• Remote

urllib3 is a user-friendly HTTP client library for Python. When using urllib3's proxy support with `ProxyManager`, the `Proxy-Authorization` header is only sent to the configured proxy, as expected. However, when sending HTTP requests *without* using urllib3's proxy support, it's possible to accidentally configure the `Proxy-Authorization` header even though it won't have any effect as the request is not using a forwarding proxy or a tunneling proxy. In those cases, urllib3 doesn't treat the `Proxy-Authorization` HTTP header as one carrying authentication material and thus doesn't strip the header on cross-origin redirects. Because this is a highly unlikely scenario, we believe the severity of this vulnerability is low for almost all users. Out of an abundance of caution urllib3 will automatically strip the `Proxy-Authorization` header during cross-origin redirects to avoid the small chance that users are doing this on accident. Users should use urllib3's proxy support or disable automatic redirects to achieve safe processing of the `Proxy-Authorization` header, but we still decided to strip the header by default in order to further protect users who aren't using the correct approach. We believe the number of usages affected by this advisory is low. It requires all of the following to be true to be exploited: 1. Setting the `Proxy-Authorization` header without using urllib3's built-in proxy support. 2. Not disabling HTTP redirects. 3. Either not using an HTTPS origin server or for the proxy or target origin to redirect to a malicious origin. Users are advised to update to either version 1.26.19 or version 2.2.2. Users unable to upgrade may use the `Proxy-Authorization` header with urllib3's `ProxyManager`, disable HTTP redirects using `redirects=False` when sending requests, or not user the `Proxy-Authorization` header as mitigations.

CVE

CVE-2024-37891

CWE

CWE-669

CVSS base score

6.5

Published

2024-06-17

OWASP

A07 Identification and Authentication Failures

Orthogonal defect classification

Checking

Code defect classification

Incorrect Check

Category

Authentication, Authorization, and Session Management

Subcategory

Session Management Issues

Accessibility scope

Remote

Impact

Unauthorized Access

Affected component

urllib3

Fixed by upgrading

Yes

Solution

Upgrade to urllib3 version 1.26.19 or 2.2.2.

import urllib3

http = urllib3.PoolManager()

headers = {
    'Proxy-Authorization': 'Basic dXNlcm5hbWU6cGFzc3dvcmQ='
}

response = http.request('GET', 'http://example.com', headers=headers)

print(response.data)

import urllib3
import ssl
from urllib.parse import urlparse

http = urllib3.PoolManager(
    cert_reqs='CERT_REQUIRED',
    ssl_context=ssl.create_default_context()
)

def check_url(url):
    parsed_url = urlparse(url)
    return parsed_url.scheme in ['http', 'https'] and not parsed_url.netloc.startswith('localhost')

url = 'https://example.com'

if check_url(url):
    headers = {
        'Proxy-Authorization': 'Basic dXNlcm5hbWU6cGFzc3dvcmQ='
    }

    response = http.request('GET', url, headers=headers)
    print(response.data)
else:
    print("The URL is not safe for requests.")

headers = {
    'Proxy-Authorization': 'Basic dXNlcm5hbWU6cGFzc3dvcmQ='  # Example base64 encoded credentials
}

response = http.request('GET', 'http://example.com', headers=headers)

@misc{vaitp:cve202437891,
  title        = {{Improper handling of `Proxy-Authorization` header in urllib3 may expose users.}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2024},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2024-37891},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2024-37891/}}
}