Executive Summary

The vulnerability exists in pam_usb versions prior to 0.9.0, which provides hardware authentication for Linux using ordinary removable media. Several pam_usb helper tools resolved external binaries through the PATH environment variable instead of using absolute paths. This means that an attacker who can influence the process environment during PAM authentication or tool execution could substitute malicious binaries, potentially compromising the authentication process.

• Affected tools include pamusb-check, pamusb-conf, and pamusb-keyring-unlock-gnome.
• The issue is fixed in version 0.9.0 by using absolute paths for external binaries.

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Compliance Impact

The vulnerability in pam_usb allows an attacker with local access to manipulate the PATH environment variable during PAM authentication or tool execution, potentially substituting malicious binaries. This can lead to privilege escalation and unauthorized access.

Such unauthorized access and privilege escalation risks could impact compliance with standards like GDPR and HIPAA, which require strict controls on authentication mechanisms and protection of sensitive data. If exploited, this vulnerability could lead to unauthorized disclosure or modification of sensitive information, violating confidentiality and integrity requirements.

The vulnerability has been fixed in version 0.9.0 by using absolute paths for external binaries and improving secure handling of authentication data, thereby mitigating the risk and helping maintain compliance with security standards.

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Detection Guidance

This vulnerability involves the use of insecure PATH environment variable resolution in pam_usb helper tools, which can be detected by checking if the affected tools (pamusb-check, pamusb-conf, pamusb-keyring-unlock-gnome) are calling external binaries via relative paths instead of absolute paths.

To detect the vulnerability on your system, you can verify the version of pam_usb installed and inspect the relevant scripts or binaries for usage of absolute paths.

Suggested commands include:

• Check the installed pam_usb version: `pamusb-check --version` or check package manager info.
• Search for usage of relative paths in pam_usb helper tools, for example:
• Use grep to find calls to external commands without absolute paths in the pam_usb scripts: `grep -E '\b(pamusb-check|id|logger|stat|awk|sed|pidof|kill|gnome-keyring-daemon)\b' /path/to/pam_usb/tools/*`
• Check environment variables during PAM authentication to see if PATH can be manipulated.
• Review running processes for suspicious command executions or environment variables that could indicate exploitation.

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Impact Analysis

This vulnerability can allow an attacker with the ability to influence the environment during PAM authentication to execute malicious binaries instead of legitimate ones. This could lead to unauthorized access or privilege escalation on the affected Linux system, compromising the security and integrity of the authentication process.

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Mitigation Strategies

To mitigate this vulnerability, upgrade pam_usb to version 0.9.0 or later, where the issue is fixed.

Avoid using versions prior to 0.9.0, as they resolve external binaries through the PATH environment variable, which can be exploited by attackers.

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