Executive Summary

The vulnerability exists in pam_usb versions prior to 0.8.7, specifically in the src/tmux.c file. The code reads the user's $TMUX environment variable, splits it on commas, and directly inserts the socket-path component into a shell command executed by popen(). Because this value is placed inside double quotes without proper sanitization, an attacker can inject arbitrary shell commands by including a double-quote character in the environment variable. Since popen() runs with root privileges inside the PAM stack, this allows for privilege escalation through command injection.

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Impact Analysis

This vulnerability can lead to a serious security impact because it allows an attacker with limited privileges to execute arbitrary commands as root. This can result in full system compromise, including unauthorized access, data modification, or denial of service. Since the vulnerability involves command injection in a component that handles authentication, it undermines the security of the authentication process itself.

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Mitigation Strategies

To mitigate this vulnerability, upgrade pam_usb to version 0.8.7 or later, where the issue has been fixed.

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Compliance Impact

This vulnerability allows an attacker to execute arbitrary commands as root, potentially leading to unauthorized access, data breaches, and system compromise.

Such unauthorized access and potential data exposure can negatively impact compliance with common standards and regulations like GDPR and HIPAA, which require protection of sensitive data and strict access controls.

Because the vulnerability affects confidentiality, integrity, and availability, organizations using vulnerable versions of pam_usb may face increased risk of non-compliance due to failure to adequately protect user data and system integrity.

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Detection Guidance

This vulnerability can be detected by identifying systems running pam_usb versions prior to 0.8.7, as these versions contain the vulnerable code handling the $TMUX environment variable unsafely.

To detect the vulnerable version, you can check the installed pam_usb version with commands like:

• dpkg -l | grep pam_usb # On Debian-based systems
• rpm -qa | grep pam_usb # On Red Hat-based systems

Additionally, you can check for the presence of the vulnerable source file or binary and verify if the system uses pam_usb for authentication by inspecting PAM configuration files, such as /etc/pam.d/common-auth or equivalent.

Since the vulnerability involves the $TMUX environment variable being passed unsanitized to a shell command, monitoring for suspicious or unexpected values of $TMUX in user sessions or logs might help detect exploitation attempts.

No specific detection commands for the injection itself are provided, but ensuring the system is updated to pam_usb version 0.8.7 or later is the recommended mitigation.

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