CVE-2004-0126 in FreeBSD
Summary
by MITRE
The jail_attach system call in FreeBSD 5.1 and 5.2 changes the directory of a calling process even if the process doesn t have permission to change directory, which allows local users to gain read/write privileges to files and directories within another jail.
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Analysis
by VulDB Data Team • 06/27/2019
The vulnerability described in CVE-2004-0126 represents a critical privilege escalation flaw within the FreeBSD operating system's jail implementation. This issue affects FreeBSD versions 5.1 and 5.2, where the jail_attach system call fails to properly validate directory change permissions before executing the directory transition. The flaw exists in the kernel-level implementation of the jail mechanism, which is designed to isolate processes within contained environments while maintaining system security boundaries. When a local user invokes the jail_attach system call, the system incorrectly permits directory changes regardless of the process's permission level, creating a fundamental breach in the security model that separates jail environments from the host system.
The technical implementation of this vulnerability stems from inadequate access control validation within the jail subsystem. Specifically, the jail_attach system call does not perform proper permission checks before allowing a process to change its working directory to a location within another jail's filesystem namespace. This oversight allows a malicious user within a jail to manipulate their process's directory context to point to directories belonging to other jails or the host system. The flaw operates at the kernel level and leverages the existing jail infrastructure rather than introducing new attack vectors, making it particularly insidious as it exploits the legitimate functionality of the system's containment mechanisms.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass complete compromise of the jail isolation model. Local users can leverage this flaw to gain read and write access to files and directories that should remain protected within other jail environments. This capability effectively nullifies the security boundaries that jails are designed to maintain, allowing attackers to access sensitive data, modify system files, or even escalate their privileges to root level access within the compromised jail environments. The vulnerability particularly affects multi-tenant systems where multiple users operate within separate jail environments, as it enables unauthorized cross-contamination between these security domains.
This vulnerability maps directly to CWE-276, which describes improper permissions for a resource, and aligns with ATT&CK technique T1068, which covers local privilege escalation. The flaw demonstrates a classic case of insufficient privilege checking in kernel-level system calls, where the security model assumes that legitimate system calls will not be misused to gain unauthorized access. Mitigation strategies should focus on immediate patching of affected FreeBSD versions, as well as implementing additional monitoring for unauthorized directory changes within jail environments. System administrators should also consider implementing more restrictive jail configurations and regularly auditing process directory transitions to detect potential exploitation attempts. The vulnerability highlights the critical importance of proper access control validation in kernel subsystems and the need for comprehensive security testing of system call interfaces that handle privilege transitions and resource access control.