CVE-2012-2251 in rssh
Summary
by MITRE
rssh 2.3.2, as used by Debian, Fedora, and others, when the rsync protocol is enabled, allows local users to bypass intended restricted shell access via a (1) "-e" or (2) "--" command line option.
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Analysis
by VulDB Data Team • 12/21/2021
The vulnerability identified as CVE-2012-2251 affects rssh version 2.3.2, a restricted shell implementation commonly deployed across various Linux distributions including Debian and Fedora. This flaw exists within the rsync protocol implementation of rssh, creating a critical security bypass opportunity for local users who possess access to the system. The vulnerability specifically manifests when rsync protocol functionality is enabled, allowing attackers to exploit command line option handling to circumvent the intended restrictions that should limit user access to only specific shell commands.
The technical implementation of this vulnerability stems from improper validation of command line arguments within rssh's rsync protocol handling code. When users provide the "-e" or "--" command line options, the system fails to properly sanitize or validate these inputs against the restricted shell environment. This allows malicious users to inject additional commands or parameters that bypass the normal access controls, effectively breaking out of the restricted shell context and gaining access to full shell capabilities. The flaw represents a classic command injection vulnerability where user-supplied parameters are not adequately filtered or escaped before being processed by the underlying shell mechanisms.
The operational impact of this vulnerability is significant as it transforms a controlled restricted shell environment into a potential attack vector for privilege escalation. Local users who can execute commands through the rssh interface can exploit this flaw to execute arbitrary commands with elevated privileges, potentially leading to complete system compromise. The vulnerability affects systems where rssh is configured to use rsync protocol, which is common in environments where users need controlled access to file synchronization operations. This creates a dangerous situation where legitimate administrative access controls are bypassed, allowing unauthorized command execution within the restricted shell context.
Security mitigations for this vulnerability should focus on immediate patching of affected rssh installations to versions that properly validate command line arguments and implement stricter input sanitization. Organizations should also consider implementing additional monitoring and logging of rssh usage to detect potential exploitation attempts. The vulnerability aligns with CWE-78, which describes improper neutralization of special elements used in OS commands, and maps to ATT&CK technique T1059.001 for command and scripting interpreter. System administrators should also review and restrict rsync protocol usage where possible, as the vulnerability specifically requires this protocol to be enabled to be exploitable. Regular security audits of restricted shell configurations are essential to prevent similar issues from arising in other similar implementations.