CVE-2003-1161 in Linux
Summary
by MITRE
exit.c in Linux kernel 2.6-test9-CVS, as stored on kernel.bkbits.net, was modified to contain a backdoor, which could allow local users to elevate their privileges by passing __WCLONE|__WALL to the sys_wait4 function.
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Analysis
by VulDB Data Team • 06/16/2018
The vulnerability described in CVE-2003-1161 represents a critical backdoor implementation within the Linux kernel version 2.6-test9-CVS, specifically targeting the exit.c file that handles process termination and waiting operations. This backdoor was introduced as an intentional modification to the kernel source code, creating a covert privilege escalation mechanism that could be exploited by local attackers. The flaw operates through the sys_wait4 system call interface, which is responsible for waiting for child processes to terminate and retrieving their status information. The backdoor specifically leverages the __WCLONE and __WALL flags that are typically used for process waiting operations, but in this malicious implementation, these flags serve as trigger mechanisms for unauthorized privilege elevation.
The technical implementation of this vulnerability exploits the kernel's process management subsystem by manipulating the wait4 system call to bypass normal security checks and privilege validation mechanisms. When a local user invokes sys_wait4 with the specially crafted __WCLONE|__WALL flag combination, the modified kernel code recognizes this pattern and executes unauthorized privilege escalation routines. This attack vector represents a sophisticated form of kernel-level privilege escalation that operates below the detection capabilities of standard security monitoring systems. The vulnerability falls under CWE-284, which addresses improper access control in software systems, and specifically demonstrates how intentional backdoors can compromise even the most fundamental security primitives within operating system kernels.
The operational impact of CVE-2003-1161 is severe and far-reaching, as it provides local attackers with a reliable method to gain root privileges on affected systems without requiring any network access or external exploitation vectors. This local privilege escalation vulnerability can be exploited by any user with access to the system, making it particularly dangerous in multi-user environments where users may not have elevated privileges. The backdoor operates silently in the kernel space, making it difficult to detect through conventional forensic analysis or intrusion detection systems. Once exploited, the attacker gains complete control over the system, including the ability to modify kernel code, access sensitive data, and establish persistent access mechanisms. This vulnerability directly violates the principle of least privilege and undermines the fundamental security model of the Linux operating system.
Mitigation strategies for this vulnerability require immediate system hardening measures and comprehensive security assessments. The most effective immediate solution involves patching the kernel with the official security update that removes the backdoor code and restores proper privilege validation mechanisms. System administrators should also implement comprehensive monitoring of kernel system calls, particularly around wait4 operations, to detect any suspicious usage patterns. Additionally, the use of kernel integrity checking tools such as tripwire or AIDE can help identify unauthorized modifications to kernel source code or compiled binaries. Organizations should conduct thorough security audits to ensure that no other backdoors or malicious modifications exist in their kernel installations, as this vulnerability demonstrates how attackers can introduce persistent access mechanisms at the kernel level. The incident also highlights the importance of maintaining secure development practices and source code integrity verification processes that prevent unauthorized modifications to critical system components.