CVE-2012-3478 in rssh
Summary
by MITRE
rssh 2.3.3 and earlier allows local users to bypass intended restricted shell access via crafted environment variables in the command line.
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Analysis
by VulDB Data Team • 12/12/2021
The vulnerability identified as CVE-2012-3478 affects rssh version 2.3.3 and earlier, representing a critical security flaw in restricted shell implementations. This issue resides within the command line parsing mechanism of rssh, which is designed to provide limited shell access to users while restricting their ability to execute potentially dangerous commands. The vulnerability stems from insufficient validation of environment variables passed through command line arguments, creating a pathway for local attackers to circumvent the intended access restrictions. The flaw specifically targets the security model that relies on environment variable handling to maintain shell confinement, making it particularly dangerous in multi-user environments where privilege separation is critical.
The technical implementation of this vulnerability exploits the way rssh processes environment variables during command execution. When users connect to the restricted shell, the system typically sets specific environment variables to enforce access controls and command limitations. However, in affected versions, maliciously crafted environment variables can be passed through command line arguments that override or bypass these security mechanisms. This occurs because the software fails to properly sanitize or validate environment variable contents before incorporating them into the shell execution context. The vulnerability is particularly insidious because it operates at the level of environment variable injection rather than direct command execution, making it more difficult to detect through standard input validation measures.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass complete bypass of restricted shell controls. Local users who can manipulate command line arguments gain the ability to execute arbitrary commands within the restricted shell environment, potentially compromising the entire system. This flaw undermines the fundamental security premise of restricted shells, which are commonly deployed in scenarios requiring controlled access to system resources such as automated backup systems, database access points, or remote administration interfaces. The vulnerability affects systems where rssh is used to provide limited access to users who should not have full shell privileges, creating potential data exfiltration, system modification, or lateral movement capabilities for attackers who can execute local commands.
Mitigation strategies for CVE-2012-3478 must address both immediate remediation and long-term security hardening. The primary recommendation involves upgrading to rssh version 2.3.4 or later, where the vulnerability has been patched through enhanced environment variable validation and proper sanitization of command line inputs. Organizations should also implement comprehensive environment variable filtering mechanisms that prevent unauthorized modifications to critical shell parameters. This vulnerability aligns with CWE-77 and CWE-20 categories, representing command injection and input validation weaknesses respectively, and maps to ATT&CK techniques such as T1059 for command and script execution and T1548.1 for abuse of privileged communication channels. Additional defensive measures include implementing strict access controls, monitoring for unusual environment variable modifications, and conducting regular security audits of restricted shell configurations to prevent similar vulnerabilities from emerging in other components of the system architecture.