CVE-2016-6902 in lshell
Summary
by MITRE
lshell 0.9.16 allows remote authenticated users to break out of a limited shell and execute arbitrary commands.
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Analysis
by VulDB Data Team • 12/02/2022
The vulnerability identified as CVE-2016-6902 affects lshell version 0.9.16, a limited shell designed to restrict user access to specific commands and prevent unauthorized system exploitation. This security flaw represents a critical breakout vulnerability that undermines the fundamental security premise of the application. The issue manifests when authenticated remote users can manipulate the shell environment to escape the intended restrictions and execute arbitrary commands with elevated privileges. Such a vulnerability directly violates the core principle of privilege separation and access control that lshell is designed to enforce, creating a significant risk for systems relying on this security mechanism.
The technical implementation of this vulnerability stems from improper input validation and command execution handling within the lshell application. When users authenticate and interact with the limited shell environment, the system fails to properly sanitize or validate user inputs before processing them through shell command execution mechanisms. This allows attackers to craft specific input sequences that bypass the intended command filtering and restriction policies. The flaw essentially creates a path where legitimate shell functionality can be leveraged to execute unintended system commands, effectively nullifying the protective measures that lshell is meant to provide. The vulnerability operates at the intersection of command injection and privilege escalation, where the authenticated user's access rights are exploited to gain broader system control.
The operational impact of this vulnerability extends beyond simple command execution, as it fundamentally compromises the security architecture of systems using lshell for user access control. Attackers can leverage this vulnerability to escalate privileges, access restricted system resources, modify critical files, and potentially establish persistent backdoors within the compromised environment. The authenticated nature of the exploit means that legitimate users with valid credentials can be used to gain unauthorized access, making this vulnerability particularly dangerous in environments where multiple users have access to the system. Organizations relying on lshell for security isolation may experience complete compromise of their access control policies, leading to potential data breaches, system infiltration, and unauthorized administrative access.
Mitigation strategies for CVE-2016-6902 require immediate action including the application of available patches or updates to lshell version 0.9.17 and later, which address the input validation issues that enable command injection. System administrators should implement additional monitoring and logging mechanisms to detect suspicious command execution patterns that may indicate exploitation attempts. The principle of least privilege should be enforced by limiting the number of users with authenticated access to systems running lshell, and implementing supplementary security controls such as network segmentation and intrusion detection systems. Organizations should also consider alternative access control mechanisms that do not rely on single-point security solutions, implementing multi-layered security approaches that reduce the impact of individual vulnerabilities. This vulnerability aligns with CWE-77 and CWE-20 categories related to command injection and input validation failures, and represents a technique that could be mapped to ATT&CK tactics including privilege escalation and command and control operations.