Mitigation Strategies

To mitigate this vulnerability, avoid using the uutils coreutils tail command with the --follow=name option in environments where untrusted users have write access to directories being monitored.

Specifically, do not allow local attackers with write permissions to replace monitored files with symbolic links, as this can lead to disclosure of sensitive file contents.

Consider using the GNU tail implementation instead, which detects and refuses to follow symbolic link replacements, preventing this type of information disclosure.

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Executive Summary

This vulnerability exists in the tail utility of uutils coreutils when using the --follow=name option. Unlike the GNU tail implementation, uutils tail continues to monitor a file path even after it has been replaced by a symbolic link. This behavior allows a local attacker with write access to a monitored log directory to replace a log file with a symbolic link pointing to a sensitive system file, such as /etc/shadow. As a result, the tail utility discloses the contents of the sensitive file.

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Impact Analysis

The vulnerability can lead to unauthorized disclosure of sensitive file contents. In environments where a privileged user monitors log files using uutils tail with the --follow=name option, a local attacker can exploit this flaw to read sensitive system files by replacing log files with symbolic links. This can result in exposure of critical information such as password hashes, potentially leading to privilege escalation or further system compromise.

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Compliance Impact

This vulnerability allows a local attacker with write access to a monitored log directory to exfiltrate sensitive file contents by exploiting the tail utility's handling of symbolic links. Such unauthorized disclosure of sensitive information could lead to violations of data protection regulations and standards that require the confidentiality and integrity of sensitive data, such as GDPR and HIPAA.

Specifically, if sensitive files like /etc/shadow are disclosed, it could result in non-compliance with regulations that mandate protection of personal or sensitive information, potentially leading to legal and financial consequences.

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Detection Guidance

This vulnerability can be detected by testing the behavior of the uutils tail command with the --follow=name option when a file is replaced by a symbolic link.

A suggested test involves the following steps:

• Create a directory and a file named 'testfile' containing some text, e.g., "original".
• Run the command: tail --follow=name testfile (optionally with a timeout).
• Remove 'testfile' and replace it with a symbolic link to a sensitive file, such as /etc/passwd.
• Observe the output: if the tail command continues to output the contents of the symlink target file, the vulnerability is present.

This behavior differs from GNU tail, which refuses to follow the symlink and outputs a message indicating the file has been replaced with an untailable symbolic link.

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