CVE-2021-46903

Executive Summary

CVE-2021-46903 is a critical access control vulnerability in Meinberg LANTIME-Firmware, specifically within the LTOS-Web-Interface. The flaw allows an authenticated administrator to delete required user accounts, violating expected access control policies. This can lead to a denial of service (DoS) or privilege escalation if critical accounts (e.g., root, admin) are removed, potentially locking out legitimate administrators or disrupting system management. The vulnerability affects firmware versions before 6.24.029 (for the 6.x branch) and before 7.04.008 (for the 7.x branch). No public exploit code or proof-of-concept is currently available, but the risk is elevated due to the administrative nature of the action.

Supply Chain & Package Security

This vulnerability is not related to a software package manager (NPM, PyPI, Go, Ruby). It is a firmware-level issue in Meinberg’s proprietary LANTIME operating system. No supply chain implications are identified.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (No official CVSS vector assigned by NVD)
• Threat Level: Medium to High (based on impact)
• Attack Vector: Network (admin interface)
• Attack Complexity: Low
• Privileges Required: High (admin)
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: None (directly)
• Integrity Impact: High (deletion of user accounts)
• Availability Impact: High (potential DoS if critical accounts removed)

Deep Dive & Mechanics

The vulnerability resides in the LTOS-Web-Interface, the web-based management console for Meinberg LANTIME devices. The interface allows administrators to manage user accounts. Due to a missing authorization check, an admin can delete any user account, including those that are required for system operation (e.g., the default admin account or system service accounts). This violates the principle of least privilege and expected access control, as the system should prevent deletion of accounts that are essential for system management or authentication.

The root cause is a lack of validation in the account deletion endpoint. The code does not check if the target account is a "protected" or "required" account before processing the deletion request. This allows an admin to inadvertently or maliciously lock themselves or other legitimate users out of the system.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// Vulnerable endpoint - no check for protected accounts
app.delete('/api/users/:id', (req, res) => {
    const userId = req.params.id;
    // Direct deletion without checking if user is required
    db.users.delete(userId);
    res.status(200).send('User deleted');
});

Patched Code (Conceptual):

// Patched endpoint - checks for protected accounts
app.delete('/api/users/:id', (req, res) => {
    const userId = req.params.id;
    const user = db.users.get(userId);
    if (user && user.isProtected) {
        return res.status(403).send('Cannot delete protected user');
    }
    db.users.delete(userId);
    res.status(200).send('User deleted');
});

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to a Meinberg LANTIME device with vulnerable firmware (e.g., version 6.20.000).
• Valid admin credentials (e.g., admin:admin).

Exploitation Steps:

1. Log in to the LTOS-Web-Interface as an admin.
2. Navigate to the user management section (e.g., /admin/users).
3. Identify a required user account (e.g., root or admin).
4. Send a DELETE request to the API endpoint:

   DELETE /api/users/1 HTTP/1.1
   Host: target-device
   Cookie: session=admin-session-token
   

5. Confirm deletion. The account is removed, potentially locking out other admins.

Impact: Denial of service, privilege escalation, or complete loss of administrative access.

Blue Team

Detection:

• Monitor for DELETE requests to /api/users/* endpoints.
• Alert on deletion of accounts with high privilege levels (e.g., admin, root).
• Log all user management actions with source IP and user agent.

Prevention:

• Apply the vendor patch immediately.
• Implement additional access controls (e.g., multi-factor authentication for admin actions).
• Restrict admin access to trusted IPs only.

Indicators of Compromise (IOCs)

• Network: HTTP DELETE requests to /api/users/* from admin sessions.
• Logs: Audit log entries showing deletion of user accounts with high privilege levels.
• System: Missing critical user accounts (e.g., admin, root) in the user database.
• File: Changes to /etc/shadow or equivalent user database files.

Detection Engineering

YARA Rule

rule CVE_2021_46903_Account_Deletion {
    meta:
        description = "Detects attempts to delete user accounts via LTOS-Web-Interface"
        author = "Valters IT"
        date = "2025-04-17"
        reference = "CVE-2021-46903"
    strings:
        $s1 = "DELETE /api/users/" ascii wide nocase
        $s2 = "User deleted" ascii wide nocase
    condition:
        any of them
}

Sigma Rule

title: CVE-2021-46903 - Admin Account Deletion in Meinberg LANTIME
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects deletion of user accounts via LTOS-Web-Interface
author: Valters IT
date: 2025-04-17
logsource:
    category: web
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: 'DELETE'
        cs-uri-stem: '/api/users/*'
    condition: selection
falsepositives:
    - Legitimate admin actions (should be rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2021-46903 - Admin Account Deletion Attempt"; flow:to_server; http.method; content:"DELETE"; http.uri; content:"/api/users/"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade LANTIME-Firmware to version 6.24.029 MBGID-9343 (for 6.x) or 7.04.008 MBGID-6303 (for 7.x).
2. If patching is not possible, restrict admin access to trusted IPs and implement strict monitoring.

Long-term Measures:

• Implement role-based access control (RBAC) to prevent deletion of critical accounts.
• Add confirmation dialogs for destructive actions.
• Conduct regular security audits of web interfaces.

Workarounds:

• Disable the user management API if not required.
• Use network segmentation to limit access to the management interface.

Valters IT