CVE-2023-36456

Unverified X-Forwarded-For and X-Real-IP headers in authentik (prior to 2023.4.3 and 2023.5.5)

• CVSS 7.3
• CWE-436 Interpretation Conflict
• Authentication, Authorization, and Session Management
• Remote

authentik is an open-source Identity Provider. Prior to versions 2023.4.3 and 2023.5.5, authentik does not verify the source of the X-Forwarded-For and X-Real-IP headers, both in the Python code and the go code. Only authentik setups that are directly accessible by users without a reverse proxy are susceptible to this. Possible spoofing of IP addresses in logs, downstream applications proxied by (built in) outpost, IP bypassing in custom flows if used. This poses a possible security risk when someone has flows or policies that check the user's IP address, e.g. when they want to ignore the user's 2 factor authentication when the user is connected to the company network. A second security risk is that the IP addresses in the logfiles and user sessions are not reliable anymore. Anybody can spoof this address and one cannot verify that the user has logged in from the IP address that is in their account's log. A third risk is that this header is passed on to the proxied application behind an outpost. The application may do any kind of verification, logging, blocking or rate limiting based on the IP address, and this IP address can be overridden by anybody that want to. Versions 2023.4.3 and 2023.5.5 contain a patch for this issue.

CVE

CVE-2023-36456

CWE

CWE-436 Interpretation Conflict

CVSS base score

7.3

Published

2023-07-06

OWASP

A07 Identification and Authentication Failures

Orthogonal defect classification

Function

Code defect classification

Incorrect Functionality

Category

Authentication, Authorization, and Session Management

Subcategory

Insecure Authentication Mechanisms

Accessibility scope

Remote

Impact

Unauthorized Access

Fixed by upgrading

Yes

Solution

Update to authentik versions 2023.4.3 or 2023.5.5 or higher.

from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route('/some_endpoint', methods=['GET'])
def some_endpoint():
    client_ip = request.headers.get('X-Forwarded-For', request.remote_addr)
    
    print(f"Client IP: {client_ip}")
    
    return jsonify({"client_ip": client_ip}), 200

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

from flask import Flask, request, jsonify
import ipaddress

app = Flask(__name__)

def get_client_ip():
    x_forwarded_for = request.headers.get('X-Forwarded-For')
    if x_forwarded_for:
        ip = x_forwarded_for.split(',')[0].strip()
    else:
        ip = request.remote_addr

    if validate_ip(ip):
        return ip
    else:
        return None

def validate_ip(ip):
    try:
        ipaddress.ip_address(ip)
        return True
    except ValueError:
        return False

@app.route('/some_endpoint', methods=['GET'])
def some_endpoint():
    client_ip = get_client_ip()
    if client_ip:
        return jsonify({"client_ip": client_ip}), 200
    else:
        return jsonify({"error": "Invalid IP address"}), 400

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

@misc{vaitp:cve202336456,
  title        = {{Unverified X-Forwarded-For and X-Real-IP headers in authentik (prior to 2023.4.3 and 2023.5.5)}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2023},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2023-36456},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2023-36456/}}
}