CVE-2016-2568 in pkexec
Summary
by MITRE
pkexec, when used with --user nonpriv, allows local users to escape to the parent session via a crafted TIOCSTI ioctl call, which pushes characters to the terminal's input buffer.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 09/01/2020
The vulnerability identified as CVE-2016-2568 affects the pkexec utility, a component of the polkit package commonly found in linux distributions. This flaw exists in the privilege execution mechanism that allows users to execute commands with elevated privileges. The vulnerability specifically manifests when pkexec is invoked with the --user parameter specifying a non-privileged user account. The issue stems from inadequate input validation and handling within the ioctl system call processing, particularly the TIOCSTI ioctl command which is designed to inject characters into terminal input buffers.
The technical exploitation of this vulnerability relies on the ability of a local attacker to craft a malicious TIOCSTI ioctl call that can manipulate the terminal input buffer of the parent session. When pkexec operates with --user nonpriv, it creates a scenario where the utility maintains a connection to the parent terminal session. The flaw occurs because the system does not properly sanitize or validate the input data passed through the ioctl mechanism, allowing an attacker to inject arbitrary terminal characters. This injection can potentially be leveraged to execute commands in the context of the parent session, effectively bypassing the intended privilege separation.
The operational impact of this vulnerability is significant for system security as it enables local privilege escalation attacks. An attacker with access to a non-privileged account can potentially escape the restricted execution environment and gain access to the parent session's privileges. This creates a vector for attackers to escalate their privileges without requiring additional authentication mechanisms or complex exploitation techniques. The vulnerability essentially undermines the fundamental security principle of privilege separation that pkexec is designed to enforce. The attack requires local access to the system but does not necessitate network connectivity or complex exploitation chains, making it particularly dangerous in multi-user environments.
Mitigation strategies for CVE-2016-2568 should focus on updating the affected pkexec implementation to a patched version that properly validates and sanitizes ioctl input parameters. System administrators should ensure that all polkit packages are updated to versions that address this specific vulnerability. Additionally, implementing proper access controls and monitoring for suspicious ioctl activity can help detect potential exploitation attempts. The vulnerability aligns with CWE-119 which deals with insufficient protection of data structures and CWE-20 which addresses input validation issues. From an ATT&CK perspective, this vulnerability maps to privilege escalation techniques and can be categorized under T1068 which involves exploiting vulnerabilities in operating systems. Organizations should also consider implementing least privilege principles and regularly auditing privilege execution mechanisms to prevent similar issues from arising in other components of their security infrastructure.