How to remediate – Hydra: HTTP proxy

1. Introduction

Hydra: HTTP proxy is a vulnerability where an attacker may be able to determine HTTP proxy passwords through brute force attacks. This poses a risk to business confidentiality, integrity and availability as compromised proxies can intercept sensitive data, modify traffic, or disrupt network services. Systems running HTTP proxy servers are typically affected. Impact on confidentiality is high due to potential data interception; impact on integrity is medium if attackers can manipulate traffic; and impact on availability is low unless the proxy server itself is disrupted.

2. Technical Explanation

This vulnerability occurs when HTTP proxy authentication relies on weak or guessable passwords, allowing an attacker to use brute-force techniques like Hydra to crack them. The attacker needs a list of potential usernames and passwords. Successful exploitation grants access to the proxy server and all traffic passing through it. CVE-2017-9805 describes similar vulnerabilities in various HTTP proxies. An example attack involves using Hydra with a wordlist containing common credentials against the target proxy server.

• Root cause: Weak or default passwords used for HTTP proxy authentication.
• Exploit mechanism: Attackers use tools like Hydra to attempt multiple username/password combinations until successful authentication is achieved. Example payload: `hydra -l -P http-proxy-login`.
• Scope: HTTP proxy servers running on various platforms, including Linux and Windows, are affected if they use weak or default credentials.

3. Detection and Assessment

To confirm vulnerability, first check the proxy server configuration for weak passwords. A thorough assessment involves attempting a brute-force attack in a controlled environment.

• Quick checks: Check the proxy server’s authentication settings via its management interface or configuration files.
• Scanning: Nessus plugin ID 84673 can be used to detect HTTP proxy accounts and passwords by brute force (example only).
• Logs and evidence: Examine proxy server logs for failed login attempts originating from unusual IP addresses, particularly repeated failures with different usernames. Log files are typically located in `/var/log/nginx/` or similar directories depending on the proxy software used.

# Example command to check proxy configuration (replace with your specific proxy software)
grep -r "user" /etc/nginx/nginx.conf

4. Solution / Remediation Steps

The primary solution is to change the passwords for all affected accounts. Follow these steps to fix the issue.

4.1 Preparation

• A change window may be required to minimize impact during password updates. Approval from system owners is recommended.

4.2 Implementation

1. Step 1: Log in to the proxy server’s management interface or access its configuration files.
2. Step 2: Identify all user accounts configured for HTTP proxy authentication.
3. Step 3: Change the passwords for each account to strong, unique values (at least 12 characters with a mix of uppercase and lowercase letters, numbers, and symbols).
4. Step 4: Save the updated configuration file.
5. Step 5: Restart the proxy service to apply the changes.

4.3 Config or Code Example

Before

# nginx configuration example with weak password
http {
    proxy_pass http://backend;
    basic_auth on;
    basic_auth_user user1;
    basic_auth_password password123;
}

After

# nginx configuration example with strong password
http {
    proxy_pass http://backend;
    basic_auth on;
    basic_auth_user user1;
    basic_auth_password $6$rounds=5000$salt$hashed_password; # Use a hashed password
}

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue. Least privilege reduces the impact if an account is compromised. Strong passwords make brute-force attacks more difficult. Regular password changes limit exposure time.

• Practice 1: Implement least privilege, granting only necessary access to proxy server accounts.
• Practice 2: Enforce strong password policies requiring complex and unique credentials.

4.5 Automation (Optional)

# Example PowerShell script to update proxy passwords (replace with your specific environment)
# Requires appropriate permissions and access to the proxy server configuration
# WARNING: This is a simplified example and may need adjustments for your setup
# Get-Content -Path "C:pathtoproxy_config.txt" | ForEach-Object {
#   if ($_ -match "basic_auth_password") {
#     $newPassword = Read-Host -Prompt "Enter new password" -AsSecureString
#     $_ -replace "basic_auth_password (.*)", "basic_auth_password $newPassword"
#   } else {
#     $_
#   }
# } | Set-Content -Path "C:pathtoproxy_config.txt"

5. Verification / Validation

Confirm the fix by verifying that the new passwords are in effect and that brute-force attempts fail. Perform a smoke test to ensure proxy functionality remains intact.

• Post-fix check: Attempt to authenticate with the old password using a tool like `curl` or a web browser. Expected output: Authentication failure (401 Unauthorized).
• Re-test: Re-run the Nessus scan (plugin ID 84673) and confirm that it no longer detects weak passwords.
• Smoke test: Verify that users can still access websites through the proxy server without interruption.
• Monitoring: Monitor proxy server logs for failed login attempts, looking for any unusual activity or patterns. Example query: `grep “Authentication failure” /var/log/nginx/error.log`.

# Post-fix command and expected output (example using curl)
curl -u user1:oldpassword http://proxy_ip/
# Expected Output: 401 Unauthorized

6. Preventive Measures and Monitoring

Update security baselines to include strong password requirements for proxy servers. Implement CI/CD pipeline checks to prevent weak passwords from being deployed. Establish a regular patch or configuration review cycle.

• Baselines: Update your security baseline to enforce strong password policies and regularly audit proxy server configurations.

7. Risks, Side Effects, and Roll Back

Changing passwords may temporarily disrupt service if users have hardcoded credentials. Incorrect configuration can also prevent access. Restore the backed-up configuration file to roll back.

• Risk or side effect 2: