CVE-2014-9645 in BusyBox
Summary
by MITRE
The add_probe function in modutils/modprobe.c in BusyBox before 1.23.0 allows local users to bypass intended restrictions on loading kernel modules via a / (slash) character in a module name, as demonstrated by an "ifconfig /usbserial up" command or a "mount -t /snd_pcm none /" command.
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Analysis
by VulDB Data Team • 09/06/2020
The vulnerability identified as CVE-2014-9645 resides within the modutils/modprobe.c component of BusyBox versions prior to 1.23.0, representing a critical security flaw that undermines kernel module loading restrictions. This issue specifically targets the add_probe function which handles module name validation during kernel module loading operations. The vulnerability exploits a fundamental weakness in input sanitization that permits maliciously crafted module names containing forward slash characters to circumvent intended security controls. Attackers can leverage this weakness to execute unauthorized kernel module loading operations by embedding slash characters within module specifications, effectively bypassing the access controls that should prevent such actions.
The technical implementation of this vulnerability stems from inadequate validation of module names passed to the modprobe utility. When a user executes commands such as "ifconfig /usbserial up" or "mount -t /snd_pcm none /", the system processes these commands through the modprobe function without proper sanitization of the module name parameter. The presence of the slash character in the module specification allows the system to interpret the command in a way that bypasses the intended restriction mechanisms. This flaw operates at the intersection of privilege escalation and kernel module management, where local users can exploit the vulnerability to load unauthorized kernel modules that may provide elevated privileges or enable further exploitation.
The operational impact of CVE-2014-9645 extends beyond simple privilege escalation to encompass potential system compromise and privilege escalation within kernel space. Local attackers can utilize this vulnerability to load malicious kernel modules that could provide root access, enable kernel memory manipulation, or create persistent backdoors. The vulnerability particularly affects systems running BusyBox versions before 1.23.0 where modprobe functionality is used for module loading operations. This flaw represents a classic case of inadequate input validation that allows path traversal-like behavior within kernel module contexts, making it particularly dangerous for embedded systems and devices that rely on BusyBox for essential system functions.
The vulnerability aligns with CWE-20, which describes improper input validation, and demonstrates characteristics consistent with ATT&CK technique T1068, which involves exploitation of a remote or local service to gain system privileges. Organizations using affected BusyBox versions face significant risk as this vulnerability can be exploited by any local user to bypass kernel module restrictions. The impact is particularly severe in embedded systems, IoT devices, and appliances that rely on BusyBox for system management functions, where such devices often run with elevated privileges and may be accessible to untrusted local users. Remediation efforts must focus on updating to BusyBox 1.23.0 or later, where proper input sanitization has been implemented to prevent slash character processing in module names.
Security practitioners should implement comprehensive monitoring for suspicious modprobe usage patterns and ensure that all systems running BusyBox are updated to versions that address this vulnerability. The fix implemented in BusyBox 1.23.0 includes proper validation of module names to reject those containing slash characters, thereby preventing the bypass of intended security restrictions. Organizations should also consider implementing additional controls such as file system permissions, kernel module signing, and restricted user access to prevent exploitation of similar vulnerabilities in other components of their security infrastructure. This vulnerability highlights the importance of proper input validation in system utilities and demonstrates how seemingly minor implementation flaws can lead to significant security implications in kernel-level operations.