CVE-2019-3463 in rssh
Summary
by MITRE
Insufficient sanitization of arguments passed to rsync can bypass the restrictions imposed by rssh, a restricted shell that should restrict users to perform only rsync operations, resulting in the execution of arbitrary shell commands.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 07/06/2023
The vulnerability identified as CVE-2019-3463 represents a critical security flaw in the rsync utility that directly undermines the security model of rssh, a restricted shell designed to limit user capabilities to only rsync operations. This issue arises from inadequate input validation and sanitization mechanisms within the rsync command execution process, creating a pathway for privilege escalation and unauthorized system access. The flaw specifically targets environments where rssh is employed to enforce strict operational boundaries for users who should be limited to file synchronization activities only.
The technical root cause of this vulnerability stems from the improper handling of command-line arguments passed to rsync when invoked through rssh. When users attempt to execute rsync commands within the restricted shell environment, the argument sanitization process fails to properly validate or escape special characters and shell metacharacters that could be interpreted by the underlying shell. This insufficient sanitization allows attackers to inject malicious commands that bypass the intended restrictions imposed by rssh. The vulnerability is classified under CWE-77 and CWE-78 within the Common Weakness Enumeration framework, representing command injection flaws that enable arbitrary code execution through improper input handling.
The operational impact of CVE-2019-3463 extends beyond simple privilege escalation to encompass full system compromise when exploited effectively. An attacker who successfully exploits this vulnerability can execute arbitrary shell commands with the privileges of the restricted user account, potentially leading to lateral movement within the network, data exfiltration, or establishment of persistent backdoors. The restricted shell environment that rssh provides is fundamentally compromised, rendering the security controls ineffective and allowing unauthorized access to system resources that should remain protected. This vulnerability directly maps to ATT&CK technique T1059.001 for command and scripting interpreter, specifically shell scripting, and T1068 for exploit for privilege escalation.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term architectural improvements to prevent similar issues. The primary recommendation involves updating to the patched version of rsync that properly implements argument sanitization and validation mechanisms. Organizations should also implement additional layers of security including proper input filtering, command whitelisting, and regular security audits of restricted shell configurations. Network segmentation and principle of least privilege enforcement can help limit the potential damage from successful exploitation. The vulnerability highlights the importance of proper input validation in security-critical applications and demonstrates the necessity of thorough security testing for all components within restricted execution environments. System administrators should conduct comprehensive assessments of all systems utilizing rssh to identify and remediate similar vulnerabilities in related software components.