CVE-2016-10178 in DWR-932B
Summary
by MITRE
An issue was discovered on the D-Link DWR-932B router. HELODBG on port 39889 (UDP) launches the "/sbin/telnetd -l /bin/sh" command.
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Analysis
by VulDB Data Team • 05/16/2026
The vulnerability identified as CVE-2016-10178 affects the D-Link DWR-932B router model and represents a critical security flaw in the router's network services implementation. This issue manifests through an unauthenticated remote command execution vulnerability that exists within the HELODBG service running on UDP port 39889. The vulnerability stems from improper input validation and privilege management within the router's embedded operating system, allowing attackers to exploit a service that should remain restricted to authorized administrative access. The service operates by launching a telnet daemon with root-level privileges, creating a direct shell access vector that bypasses normal authentication mechanisms. This flaw directly violates security principles of least privilege and proper service isolation, as the telnet daemon is executed with full system privileges rather than restricted user permissions.
The technical exploitation of this vulnerability occurs through network-based attacks targeting the specific UDP port 39889 where the HELODBG service listens for incoming connections. When an attacker sends a crafted packet to this port, the router executes the command "/sbin/telnetd -l /bin/sh" which starts a telnet daemon that provides a shell prompt to any connecting client without requiring authentication. This creates an immediate and complete compromise of the router's system, allowing attackers to execute arbitrary commands with root privileges and gain full administrative control over the device. The vulnerability demonstrates a classic improper input validation issue, which aligns with CWE-20 - Improper Input Validation, and represents a privilege escalation flaw that enables unauthorized access to system-level resources. The flaw also exhibits characteristics of a remote code execution vulnerability that can be leveraged without requiring any prior authentication or network access to the device's management interface.
The operational impact of this vulnerability extends far beyond the immediate compromise of a single router device, as it enables attackers to establish persistent access points within network infrastructures. Once compromised, the DWR-932B router can serve as a launching platform for further attacks against internal network segments, potentially allowing attackers to conduct reconnaissance, redirect traffic, or use the device as a pivot point for accessing other systems. The vulnerability affects the router's fundamental security posture by creating an unauthenticated backdoor that remains active as long as the device is operational, making it particularly dangerous for enterprise environments where network segmentation and security controls are critical. This type of vulnerability represents a significant concern for cybersecurity professionals as it allows attackers to compromise network infrastructure devices without requiring specialized knowledge of the target network or physical access to the device. The impact is further amplified when considering that many organizations rely on default configurations and do not regularly update firmware on their network devices, leaving them vulnerable to such exploits for extended periods.
Organizations should implement immediate mitigations including network segmentation to isolate the affected router from critical network segments, disabling the problematic UDP port 39889 through firewall rules, and applying firmware updates from D-Link when available. The vulnerability demonstrates the importance of proper service hardening and network access controls, as it shows how a single misconfigured service can provide complete system compromise. Security teams should also conduct comprehensive network scans to identify other devices running similar services or vulnerable firmware versions, as this vulnerability may indicate broader security issues within the organization's network infrastructure. The flaw underscores the necessity of implementing proper network monitoring and intrusion detection systems to identify unauthorized access attempts and anomalous network behavior that could indicate exploitation of similar vulnerabilities. Additionally, this vulnerability highlights the importance of following security best practices such as regularly updating firmware, disabling unnecessary services, and implementing robust network access controls to prevent unauthorized access to critical network infrastructure devices. The issue also aligns with ATT&CK technique T1059 - Command and Scripting Interpreter, as it allows for remote command execution through the compromised telnet daemon service.