CVE-2012-5966 in DSL2730U
Summary
by MITRE
The restricted telnet shell on the D-Link DSL2730U router allows remote authenticated users to bypass intended command restrictions via shell metacharacters that follow a whitelisted command.
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Analysis
by VulDB Data Team • 08/12/2024
The CVE-2012-5966 vulnerability affects the D-Link DSL2730U router and represents a significant security flaw in its telnet shell implementation that enables authenticated attackers to circumvent command restrictions. This vulnerability specifically targets the router's restricted telnet shell functionality where administrators have attempted to limit user commands through whitelisting mechanisms. The flaw occurs when legitimate commands are followed by shell metacharacters that allow attackers to execute arbitrary commands beyond the intended restrictions. The vulnerability demonstrates a classic input validation failure where the system fails to properly sanitize command inputs before processing them.
The technical implementation of this vulnerability stems from improper handling of shell metacharacters within the router's command processing pipeline. When an authenticated user submits a command that includes a whitelisted command followed by shell metacharacters such as semicolons, ampersands, or other special characters, the system processes these characters without adequate validation or sanitization. This allows attackers to chain commands or inject additional shell operations that bypass the intended access controls. The vulnerability is particularly dangerous because it operates within the context of an authenticated session, meaning attackers must first establish valid credentials but can then escalate their privileges or execute unauthorized operations. The flaw aligns with CWE-77 and CWE-88 categories, which address command injection vulnerabilities and improper neutralization of special elements used in command execution contexts.
The operational impact of CVE-2012-5966 extends beyond simple unauthorized command execution, as it can enable attackers to gain full control of the router's functionality and potentially compromise the entire network infrastructure. An attacker who successfully exploits this vulnerability can execute arbitrary code on the router, modify network configurations, redirect traffic, or establish persistent access points within the network. The restricted shell environment was designed to prevent such escalations, but the vulnerability undermines this security boundary. From an adversary perspective, this vulnerability fits within ATT&CK tactic T1059 (Command and Scripting Interpreter) and technique T1059.007 (Unix Shell) as attackers can leverage shell metacharacters to execute commands in the restricted environment. The vulnerability also relates to T1068 (Exploitation for Privilege Escalation) since it allows authenticated users to gain elevated privileges within the router's operational context.
Mitigation strategies for CVE-2012-5966 must address both the immediate security gap and the underlying design flaw in the router's command processing. The most effective approach involves implementing robust input validation and sanitization mechanisms that properly handle shell metacharacters regardless of their position within command strings. Network administrators should disable telnet access entirely and migrate to more secure protocols such as SSH for remote management. Additionally, implementing proper command whitelisting with strict validation rules that prevent metacharacter injection is essential. Organizations should also consider network segmentation to limit the potential impact of any successful exploitation attempts. The vulnerability highlights the importance of defense in depth principles and demonstrates why simple access controls without proper input validation are insufficient for securing network infrastructure devices. Regular security updates and firmware patches from D-Link should be implemented promptly to address this and similar vulnerabilities in network equipment.