CVE-2024-11068: D-Link DSL6740C Auth Bypass Vulnerability

CVE-2024-11068 Overview

The D-Link DSL6740C modem contains an Incorrect Use of Privileged APIs vulnerability (CWE-648) that allows unauthenticated remote attackers to modify any user's password by leveraging exposed API endpoints. This critical firmware vulnerability grants attackers unauthorized access to Web, SSH, and Telnet services using compromised user accounts, effectively enabling complete device takeover without requiring any prior authentication.

Critical Impact

Unauthenticated remote attackers can modify any user's password on affected D-Link DSL6740C modems, granting full access to administrative interfaces including Web, SSH, and Telnet services. D-Link has announced it will not patch this vulnerability as the device has reached End-of-Life status.

Affected Products

• D-Link DSL6740C Modem (Hardware)
• D-Link DSL6740C Firmware (All versions)
• Approximately 60,000 exposed devices according to security reports

Discovery Timeline

• November 11, 2024 - CVE-2024-11068 published to NVD
• November 24, 2024 - Last updated in NVD database

Technical Details for CVE-2024-11068

Vulnerability Analysis

This vulnerability stems from improper access control implementation in the D-Link DSL6740C modem's API infrastructure. The device exposes privileged API endpoints that handle user credential management without implementing proper authentication checks. Remote attackers can directly interact with these APIs over the network to modify user passwords without providing any credentials or authentication tokens.

The exploitation mechanics are straightforward: an attacker can send crafted requests to the vulnerable API endpoints to change passwords for any user account on the device, including administrative accounts. Once the password is modified, the attacker gains legitimate access to all device services—Web management interface, SSH, and Telnet—using the newly set credentials.

This vulnerability is particularly severe because it affects network infrastructure devices that often serve as the gateway between internal networks and the internet. Compromising these devices can enable attackers to intercept traffic, modify DNS settings, pivot to internal networks, or use the device as part of a botnet. The fact that this is an End-of-Life (EOL) product with no forthcoming patches makes affected deployments permanently vulnerable.

Root Cause

The root cause of CVE-2024-11068 is the Incorrect Use of Privileged APIs (CWE-648). The firmware fails to properly restrict access to sensitive API functions responsible for user credential management. Specifically, the authentication and authorization checks that should protect these privileged operations are either missing entirely or implemented incorrectly, allowing any network-accessible client to invoke password modification functions.

This design flaw represents a fundamental security failure in the device's access control architecture. Rather than requiring authenticated sessions or proper authorization tokens before allowing credential changes, the API processes these requests from any source without validation.

Attack Vector

The attack vector for CVE-2024-11068 is network-based and requires no authentication or user interaction. An attacker with network access to the modem's management interfaces can exploit this vulnerability remotely. The attack flow involves:

1. The attacker identifies an exposed D-Link DSL6740C modem on the network or internet
2. The attacker sends crafted API requests to the vulnerable password modification endpoint
3. The API processes the request without authentication, changing the target user's password
4. The attacker authenticates to Web, SSH, or Telnet services using the modified credentials
5. Full device access is achieved, enabling further malicious activities

The vulnerability does not require any special privileges, complex attack chains, or user interaction, making it trivially exploitable at scale against internet-exposed devices.

Detection Methods for CVE-2024-11068

Indicators of Compromise

• Unexpected password changes for device user accounts, particularly administrative accounts
• Unauthorized login attempts or successful logins to Web, SSH, or Telnet management interfaces from unknown IP addresses
• Anomalous API requests to the device's management interface, especially targeting user credential endpoints
• Configuration changes made without administrator knowledge, such as modified DNS settings, firewall rules, or network configurations

Detection Strategies

• Monitor network traffic to D-Link DSL6740C devices for unusual API call patterns or requests to password management endpoints
• Implement logging on upstream network devices to capture authentication events and management interface access
• Deploy network intrusion detection systems (IDS) with signatures for known D-Link API exploitation attempts
• Conduct regular audits of device configurations to identify unauthorized changes

Monitoring Recommendations

• Establish baseline network behavior for management interface traffic and alert on deviations
• Configure SIEM systems to correlate login events with API access patterns on affected devices
• Monitor for new SSH or Telnet connections from unexpected geographic locations or IP ranges
• Review device logs regularly for authentication failures followed by successful logins, which may indicate password tampering

How to Mitigate CVE-2024-11068

Immediate Actions Required

• Isolate affected D-Link DSL6740C modems from direct internet exposure by placing them behind a firewall or VPN
• Disable remote management interfaces (Web, SSH, Telnet) if they are not essential for operations
• Implement network segmentation to restrict access to device management interfaces to trusted administrative networks only
• Begin planning for device replacement as D-Link has confirmed this EOL product will not receive security patches

Patch Information

D-Link has announced that the DSL6740C modem has reached End-of-Life (EOL) status and will not receive security patches for CVE-2024-11068. According to BleepingComputer's coverage, this affects approximately 60,000 exposed devices. Organizations using affected devices should prioritize replacement with actively supported networking equipment. Additional details are available from Taiwan CERT's Security Advisory.

Workarounds

• Restrict management interface access by configuring upstream firewall rules to block external access to the modem's Web, SSH, and Telnet ports
• If remote management is required, implement VPN access as the only method to reach the device's management interface
• Change all user passwords regularly and monitor for unauthorized changes as a detective control
• Consider deploying a separate firewall appliance in front of the affected modem to provide additional access control

# Example firewall rules to block external management access (apply on upstream device)
# Block external access to Web management interface
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP

# Block external access to SSH
iptables -A INPUT -p tcp --dport 22 -s ! 192.168.1.0/24 -j DROP

# Block external access to Telnet
iptables -A INPUT -p tcp --dport 23 -s ! 192.168.1.0/24 -j DROP