CVE-2011-2203 in Linux
Summary
by MITRE
The hfs_find_init function in the Linux kernel 2.6 allows local users to cause a denial of service (NULL pointer dereference and Oops) by mounting an HFS file system with a malformed MDB extent record.
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Analysis
by VulDB Data Team • 11/29/2021
The vulnerability described in CVE-2011-2203 represents a critical denial of service flaw within the Linux kernel's HFS file system implementation. This issue specifically affects the hfs_find_init function which is responsible for initializing file system operations when mounting HFS volumes. The vulnerability arises from inadequate input validation within the kernel's file system handling code, creating a scenario where maliciously crafted file system metadata can trigger system instability.
The technical flaw manifests when the Linux kernel attempts to process an HFS file system with a malformed MDB (Master Directory Block) extent record. The hfs_find_init function fails to properly validate the extent record structure before attempting to access its components, resulting in a NULL pointer dereference condition. This type of error constitutes a classic software bug that falls under the CWE-476 category of NULL Pointer Dereference, where the kernel code assumes that certain data structures will contain valid references when they may instead be null. The kernel's response to this condition is an immediate system Oops, which represents a kernel panic or system crash that terminates normal system operations.
The operational impact of this vulnerability is significant for systems running Linux kernels 2.6.x series that support HFS file systems. Local attackers who can mount HFS file systems with specially crafted metadata can trigger immediate system crashes, effectively causing a denial of service condition that renders the affected system unusable until manual intervention occurs. This vulnerability particularly affects systems that may automatically mount removable HFS media or systems that process untrusted file system images, making it a serious concern for both desktop and server environments. The attack requires minimal privileges since it only necessitates the ability to mount file systems, which is typically available to regular users on most systems.
The exploitability of this vulnerability is enhanced by the fact that it does not require elevated privileges beyond basic user access. Any local user with the ability to mount file systems can potentially trigger the condition, making it a particularly dangerous flaw for multi-user systems or environments where untrusted file systems might be encountered. From an ATT&CK framework perspective, this vulnerability aligns with techniques related to privilege escalation and denial of service, though it primarily functions as a denial of service vector rather than a direct privilege escalation mechanism. The vulnerability demonstrates the importance of robust input validation in kernel space code, as even seemingly benign file system metadata can cause catastrophic system failures when not properly sanitized.
Mitigation strategies for this vulnerability include applying the appropriate kernel security patches that were released to address the specific NULL pointer dereference in the hfs_find_init function. System administrators should ensure their Linux kernels are updated to versions that contain the fix, typically kernel versions 2.6.39 and later. Additionally, administrators can implement file system access controls to prevent untrusted users from mounting potentially malicious file systems, though this approach provides only partial protection. The vulnerability highlights the critical need for comprehensive input validation in kernel space code and demonstrates how seemingly minor flaws in file system parsing can have major system-wide consequences. Regular kernel updates and security monitoring remain essential practices for maintaining system stability and preventing exploitation of similar vulnerabilities in the future.