CVE-2009-3725 in Linux
Summary
by MITRE
The connector layer in the Linux kernel before 2.6.31.5 does not require the CAP_SYS_ADMIN capability for certain interaction with the (1) uvesafb, (2) pohmelfs, (3) dst, or (4) dm subsystem, which allows local users to bypass intended access restrictions and gain privileges via calls to functions in these subsystems.
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Analysis
by VulDB Data Team • 08/27/2021
The vulnerability described in CVE-2009-3725 represents a significant privilege escalation flaw within the Linux kernel's connector layer mechanism that existed prior to version 2.6.31.5. This issue affects four specific kernel subsystems including uvesafb for unified video framebuffer support, pohmelfs for the pohmelfs filesystem driver, dst for direct storage technology, and dm for device mapper subsystems. The core problem lies in the insufficient capability checks within the connector layer that governs inter-subsystem communication and interaction. These subsystems are designed to operate with elevated privileges due to their critical role in system operations, yet the connector layer failed to enforce proper capability requirements for accessing them.
The technical flaw stems from the connector layer's failure to validate whether processes attempting to interact with these subsystems possess the necessary CAP_SYS_ADMIN capability before allowing access. This capability represents one of the most privileged capabilities in the Linux security model, typically required for system-level operations such as mounting filesystems, configuring network interfaces, and managing device drivers. When the connector layer does not enforce this requirement, local attackers can exploit this weakness to make unauthorized calls to functions within these subsystems without proper authorization. The vulnerability essentially creates a backdoor path that bypasses the normal privilege checking mechanisms that should protect these critical kernel components from unauthorized access.
From an operational impact perspective, this vulnerability enables local users to escalate their privileges from standard user level to root level without requiring any special privileges or authentication. The implications are severe because any user with access to the system can leverage this flaw to gain complete administrative control over the kernel subsystems. This privilege escalation occurs silently without triggering any security alerts or audit trails, making it particularly dangerous for system administrators who rely on standard security monitoring tools. The attack vector is straightforward and requires only local execution capabilities, meaning that even unprivileged users can exploit this vulnerability to gain system-wide control.
The vulnerability aligns with CWE-269: "Improper Privilege Management" and specifically relates to CWE-782: "Exposed Runnable Scheduler" in the context of kernel subsystem interactions. It also maps to several ATT&CK techniques including T1068: "Exploitation for Privilege Escalation" and T1548.001: "Abuse Elevation Control Mechanism" where the attacker leverages existing system mechanisms to bypass normal access controls. The attack surface is particularly concerning because these subsystems are integral to core system functionality, and their compromise can lead to complete system takeover. The vulnerability affects a broad range of Linux distributions and kernel versions, making it a widespread concern for system administrators who must ensure their kernels are properly patched and updated.
Mitigation strategies primarily focus on updating the Linux kernel to version 2.6.31.5 or later where the connector layer properly enforces CAP_SYS_ADMIN capability requirements. System administrators should also implement additional security measures including restricting local user access where possible, monitoring for unusual kernel subsystem interactions, and ensuring comprehensive patch management processes are in place. The vulnerability demonstrates the critical importance of capability-based access controls in kernel security and highlights the need for rigorous validation of all inter-subsystem communication paths. Organizations should conduct vulnerability assessments to identify systems running affected kernel versions and prioritize patch deployment to prevent exploitation of this privilege escalation vulnerability.