CVE-2017-11747 in Tinyproxy
Summary
by MITRE
main.c in Tinyproxy 1.8.4 and earlier creates a /run/tinyproxy/tinyproxy.pid file after dropping privileges to a non-root account, which might allow local users to kill arbitrary processes by leveraging access to this non-root account for tinyproxy.pid modification before a root script executes a "kill `cat /run/tinyproxy/tinyproxy.pid`" command.
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Analysis
by VulDB Data Team • 12/14/2022
The vulnerability identified as CVE-2017-11747 resides within the Tinyproxy HTTP proxy server version 1.8.4 and earlier, presenting a significant privilege escalation risk through improper file handling during the service initialization process. This flaw occurs when the proxy daemon creates its process identifier file at a location that is accessible to non-root users, specifically the /run/tinyproxy/tinyproxy.pid file path. The issue stems from the software's design where it generates this critical file while still operating with elevated privileges before dropping to a non-root user account, creating a window of opportunity for malicious local users to manipulate the file contents.
The technical exploitation of this vulnerability relies on the fundamental principle of race conditions and improper privilege management within Unix-like systems. When Tinyproxy initializes and creates the pid file, it does so in a location that allows modification by the non-root user account under which the service typically runs. This creates a scenario where an attacker with access to the tinyproxy user account can modify the pid file contents before a root-level script executes a command that reads this file to determine which process to terminate. The command structure "kill `cat /run/tinyproxy/tinyproxy.pid`" becomes dangerous because it directly executes the kill command against whatever process ID is contained within the manipulated file, potentially allowing an attacker to target and terminate any process running on the system.
This vulnerability directly maps to CWE-362, which describes a race condition in privilege management, and aligns with ATT&CK technique T1068, which covers 'Local Privilege Escalation' through exploitation of process manipulation. The operational impact of this vulnerability extends beyond simple process termination, as it provides a mechanism for arbitrary process killing that could be leveraged to disrupt critical system services, disable security tools, or create denial of service conditions that could affect system availability and stability. The flaw essentially allows a local user to gain the ability to kill processes that they would normally not have permission to terminate, effectively bypassing normal Unix permission controls and privilege boundaries.
The security implications of this vulnerability are particularly concerning in multi-user environments or systems where the tinyproxy service is running with elevated privileges. Attackers could exploit this by crafting malicious pid files that point to critical system processes such as sshd, apache, or other security services, potentially leading to system compromise or service disruption. The vulnerability demonstrates poor security design principles in file creation and privilege management, where the system fails to properly isolate sensitive operations from potentially malicious user actions. Organizations should immediately update to Tinyproxy versions 1.8.5 or later, where this issue has been addressed through proper privilege separation and file creation procedures that ensure the pid file is created with appropriate permissions and ownership before any privilege dropping occurs.
Mitigation strategies should include immediate patching of affected systems, implementation of proper file permissions and ownership controls for the tinyproxy pid file location, and monitoring for unauthorized modifications to critical system files. Security administrators should also consider implementing additional controls such as file integrity monitoring solutions that can detect unauthorized changes to the pid file or related system files, as well as reviewing system logs for suspicious activity related to process termination commands. The vulnerability serves as a reminder of the importance of proper privilege management and the potential for seemingly minor design flaws to create significant security risks in system software.