CVE-2020-6765 in DSL-GS225 J1
Summary
by MITRE
D-Link DSL-GS225 J1 AU_1.0.4 devices allow an admin to execute OS commands by placing shell metacharacters after a supported CLI command, as demonstrated by ping -c1 127.0.0.1; cat/etc/passwd. The CLI is reachable by TELNET.
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Analysis
by VulDB Data Team • 10/09/2020
The vulnerability CVE-2020-6765 affects D-Link DSL-GS225 J1 AU_1.0.4 network devices, presenting a critical command injection flaw that enables unauthorized administrative execution of operating system commands. This vulnerability resides within the device's command line interface implementation, specifically when processing user input through the TELNET protocol. The flaw manifests when an attacker constructs malicious input strings that include shell metacharacters, allowing arbitrary command execution beyond the intended functionality of supported CLI commands.
This vulnerability represents a classic command injection attack vector that directly maps to CWE-77, known as "Improper Neutralization of Special Elements used in a Command ('Command Injection'). The device fails to properly sanitize or validate user input passed to the underlying operating system shell, creating an exploitable path where legitimate CLI commands can be extended with malicious payloads. The specific demonstration shows how an attacker can append shell commands to a ping utility call, effectively executing arbitrary system commands with administrative privileges.
The operational impact of this vulnerability is severe as it provides complete administrative control over affected devices. An attacker who gains access through TELNET can execute any command available to the system administrator, potentially leading to complete device compromise, data exfiltration, or use as a pivot point for further network attacks. The vulnerability affects network infrastructure devices that are typically not protected by modern security controls, making them particularly attractive targets for attackers seeking persistent access to networks.
The attack surface is expanded by the fact that TELNET remains enabled on these devices, representing a significant security weakness as TELNET transmits credentials and commands in plaintext without encryption. This vulnerability aligns with ATT&CK technique T1059.001 for Command and Scripting Interpreter, specifically focusing on the execution of system commands through legitimate interfaces. Organizations should immediately disable TELNET access and implement proper input validation mechanisms. Mitigation strategies include applying firmware updates from D-Link, implementing network segmentation to isolate affected devices, and deploying intrusion detection systems to monitor for suspicious command execution patterns. The vulnerability underscores the critical importance of input validation and the dangerous implications of legacy protocols in modern network security architectures.