CVE-2007-0166 in FreeBSD
Summary
by MITRE
The jail rc.d script in FreeBSD 5.3 up to 6.2 does not verify pathnames when writing to /var/log/console.log during a jail start-up, or when file systems are mounted or unmounted, which allows local root users to overwrite arbitrary files, or mount/unmount files, outside of the jail via a symlink attack.
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Analysis
by VulDB Data Team • 03/15/2021
The vulnerability described in CVE-2007-0166 represents a critical privilege escalation flaw within the FreeBSD operating system's jail management infrastructure. This issue affects FreeBSD versions from 5.3 through 6.2 and stems from improper pathname validation within the jail rc.d script responsible for managing jail lifecycle operations. The root cause lies in the script's failure to properly validate file paths when interacting with the console.log file during critical system operations, creating a symlink race condition that can be exploited by local users with minimal privileges to gain root access.
The technical implementation of this vulnerability exploits a classic symlink attack pattern where an attacker creates symbolic links in strategic locations to manipulate the script's behavior during jail startup or filesystem operations. When the jail rc.d script attempts to write to /var/log/console.log, it does not validate whether the target path is a legitimate file or a symbolic link pointing elsewhere in the filesystem. This lack of proper path validation creates a window of opportunity where a malicious user can pre-create symbolic links that redirect the script's output to arbitrary locations, potentially overwriting critical system files or executing unauthorized mount/unmount operations outside the intended jail boundaries.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it fundamentally undermines the security isolation that jails are designed to provide. Attackers can leverage this flaw to overwrite system binaries, configuration files, or even create persistent backdoors by manipulating the mount/unmount operations that occur during jail initialization. The vulnerability particularly affects systems running FreeBSD 5.3 through 6.2 where the jail subsystem is actively used, making it a significant concern for server environments that rely on FreeBSD's jail technology for process isolation and security containment.
This vulnerability aligns with CWE-367, which addresses the Time-of-Check to Time-of-Use (TOCTOU) race condition, and represents a classic example of how insufficient input validation can lead to privilege escalation. The attack vector follows ATT&CK technique T1068, which involves exploiting vulnerabilities in system processes to gain elevated privileges, and T1059, which covers the use of system commands to execute malicious operations. Organizations should immediately implement mitigations including updating to patched FreeBSD versions, implementing proper file system permissions for console.log files, and conducting thorough security audits of all rc.d scripts that handle critical system operations. The vulnerability also highlights the importance of proper privilege separation and input validation in system-level scripts, as even minor oversights in path validation can result in complete system compromise.