CVE-2016-4989 in setroubleshoot
Summary
by MITRE
setroubleshoot allows local users to bypass an intended container protection mechanism and execute arbitrary commands by (1) triggering an SELinux denial with a crafted file name, which is handled by the _set_tpath function in audit_data.py or via a crafted (2) local_id or (3) analysis_id field in a crafted XML document to the run_fix function in SetroubleshootFixit.py, related to the subprocess.check_output and commands.getstatusoutput functions, a different vulnerability than CVE-2016-4445.
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Analysis
by VulDB Data Team • 11/28/2022
The CVE-2016-4989 vulnerability resides within the setroubleshoot tool, a critical component of the SELinux security framework designed to help administrators diagnose and resolve SELinux policy violations. This tool serves as an interface between SELinux audit logs and user-friendly troubleshooting guidance, making it an essential element in Linux security management. The vulnerability represents a significant bypass of container protection mechanisms that are fundamental to maintaining system integrity and preventing unauthorized command execution. The flaw manifests through three distinct attack vectors that all ultimately leverage the same underlying issue of improper input validation and command execution handling within the tool's codebase.
The technical exploitation occurs through manipulation of three specific input parameters that flow through different code paths within setroubleshoot's architecture. The first vector involves triggering an SELinux denial through a crafted filename that gets processed by the _set_tpath function located in audit_data.py. This function handles path transformations that are critical for proper SELinux policy enforcement. The second and third vectors involve manipulating local_id and analysis_id fields within XML documents that are processed by the run_fix function in SetroubleshootFixit.py. All three attack paths ultimately converge on the use of subprocess.check_output and commands.getstatusoutput functions, which are notorious for creating security vulnerabilities when they receive untrusted input. This represents a classic command injection vulnerability where attacker-controlled data is passed directly to system-level command execution functions without proper sanitization.
The operational impact of this vulnerability extends far beyond simple privilege escalation, as it allows local users to bypass container protection mechanisms that are specifically designed to isolate processes and prevent unauthorized access to system resources. When exploited, the vulnerability enables attackers to execute arbitrary commands with the privileges of the setroubleshoot process, which typically runs with elevated permissions to access and modify SELinux policies. This creates a potential pathway for attackers to escalate their privileges beyond what would normally be possible within a containerized environment, effectively undermining the security boundaries that are meant to protect system integrity. The vulnerability is particularly concerning because it operates at the intersection of audit handling and policy enforcement, making it difficult to detect and remediate without comprehensive system analysis.
This vulnerability aligns with CWE-78, which describes improper neutralization of special elements used in OS command injection attacks, and demonstrates how seemingly benign input handling can create critical security weaknesses. The attack vectors also map to several ATT&CK techniques including T1059 for command and scripting interpreter and T1068 for exploit for privilege escalation. The exploitation requires local system access but does not need network connectivity, making it particularly dangerous in environments where local privilege escalation is already possible. Mitigation strategies should focus on input validation and sanitization, particularly around the subprocess functions that handle external command execution. The recommended approach involves implementing strict input validation, using safer alternatives to commands.getstatusoutput and subprocess.check_output, and ensuring that all user-provided data is properly escaped before being passed to system-level functions. Additionally, system administrators should consider restricting access to setroubleshoot functionality and implementing proper access controls to limit the potential impact of such vulnerabilities in production environments.