CVE-2012-2252 in rssh
Summary
by MITRE
Incomplete blacklist vulnerability in rssh before 2.3.4, when the rsync protocol is enabled, allows local users to bypass intended restricted shell access via the --rsh command line option.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 12/21/2021
The CVE-2012-2252 vulnerability represents a critical incomplete blacklist flaw in the rssh (restricted shell) software version 2.3.3 and earlier. This vulnerability specifically affects systems where the rsync protocol is enabled, creating a significant security gap that allows local users to circumvent the intended restricted shell access controls. The flaw resides in the software's insufficient validation mechanisms that fail to properly restrict command line options, enabling malicious users to exploit the system's trust model. The vulnerability demonstrates a classic security implementation weakness where the developers relied on a blacklist approach rather than a whitelist methodology for command line parameter validation, a pattern commonly associated with CWE-150 and CWE-151 security issues.
The technical exploitation of this vulnerability occurs through the manipulation of the --rsh command line option, which is typically used to specify a remote shell command for rsync operations. When rssh processes this option without proper validation, it fails to prevent users from specifying arbitrary shell commands that bypass the intended restricted environment. This allows attackers to execute commands outside the confines of the restricted shell, effectively escalating their privileges and gaining access to system resources that should remain unavailable. The vulnerability operates at the application layer and can be classified under ATT&CK technique T1059.001 for command and scripting interpreter, specifically targeting local users who already have access to the system. The flaw essentially transforms a controlled environment into an unrestricted one by not properly sanitizing user inputs.
The operational impact of CVE-2012-2252 extends beyond simple privilege escalation, as it fundamentally undermines the security model of restricted shell environments that are commonly deployed in multi-user systems and shared hosting environments. Organizations using rssh for user access control may experience unauthorized system access, data exfiltration, and potential lateral movement within their networks. The vulnerability is particularly dangerous in environments where rssh is used to provide limited access to system administrators or for automated backup processes, as it can enable attackers to execute arbitrary commands with elevated privileges. This represents a significant concern for system administrators who rely on restricted shells to maintain security boundaries and prevent unauthorized access to sensitive system functions.
Mitigation strategies for CVE-2012-2252 require immediate patching of affected rssh installations to version 2.3.4 or later, which contains the necessary fixes to properly validate command line parameters. System administrators should also implement additional security measures including monitoring for unauthorized use of the --rsh option, reviewing and tightening access controls for rsync operations, and considering alternative restricted shell implementations that properly implement whitelist validation. The vulnerability highlights the importance of proper input validation and the dangers of relying solely on blacklist approaches for security controls, reinforcing principles from CWE-150 that emphasize the need for robust validation mechanisms. Organizations should also consider implementing principle of least privilege practices, ensuring that rsync operations are performed with minimal required privileges and that command line options are strictly controlled to prevent arbitrary command execution.