CVE-2009-4020 in Linux
Summary
by MITRE
Stack-based buffer overflow in the hfs subsystem in the Linux kernel 2.6.32 allows remote attackers to have an unspecified impact via a crafted Hierarchical File System (HFS) filesystem, related to the hfs_readdir function in fs/hfs/dir.c.
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Analysis
by VulDB Data Team • 08/28/2021
The vulnerability identified as CVE-2009-4020 represents a critical stack-based buffer overflow within the Linux kernel's HFS subsystem, specifically affecting kernel versions up to and including 2.6.32. This flaw resides in the hfs_readdir function located in the fs/hfs/dir.c file, which processes directory read operations for Hierarchical File System volumes. The vulnerability manifests when the kernel encounters a malformed or crafted HFS filesystem, potentially enabling remote attackers to execute arbitrary code with kernel-level privileges. The stack-based nature of this buffer overflow means that attacker-controlled data can overwrite adjacent memory locations on the stack, potentially corrupting return addresses and function pointers, which could lead to complete system compromise.
The technical exploitation of this vulnerability involves crafting a malicious HFS filesystem that triggers the buffer overflow during directory traversal operations. When the hfs_readdir function processes directory entries, it fails to properly validate input parameters from the filesystem structure, allowing an attacker to supply data that exceeds the allocated buffer space. This type of vulnerability falls under CWE-121, which describes stack-based buffer overflow conditions, and aligns with ATT&CK technique T1068, which covers the exploitation of legitimate credentials and system access. The vulnerability's impact extends beyond simple code execution to potentially allow privilege escalation, as successful exploitation would enable attackers to gain kernel-level privileges and subsequently control the entire system.
From an operational standpoint, this vulnerability presents significant risks to systems that may encounter or mount HFS filesystems from untrusted sources. The remote attack vector means that an attacker could potentially compromise systems by simply providing a malicious HFS filesystem for mounting, without requiring physical access or local privileges. The unspecified impact mentioned in the CVE description suggests that the consequences could range from denial of service to complete system takeover, depending on the specific exploitation scenario and system configuration. Systems running kernel versions 2.6.32 and earlier are particularly vulnerable, as this vulnerability was addressed in subsequent kernel releases through proper input validation and buffer size checks. The flaw demonstrates the importance of robust input validation in kernel space code, as even seemingly benign filesystem operations can become attack vectors when proper bounds checking is absent.
The mitigation strategy for CVE-2009-4020 primarily involves upgrading to a patched kernel version that addresses the buffer overflow in the HFS subsystem. System administrators should prioritize updating their kernel versions to 2.6.33 or later, where the vulnerability has been resolved through proper bounds checking in the hfs_readdir function. Additionally, implementing filesystem access controls that prevent mounting of untrusted HFS volumes can provide additional defense-in-depth. Organizations should also consider monitoring for suspicious filesystem mounting activities and implementing proper network segmentation to limit the potential attack surface. The vulnerability highlights the critical importance of kernel security audits and the need for comprehensive input validation in kernel-space code, particularly for subsystems that handle external data structures such as filesystem metadata. Regular security updates and vulnerability assessments are essential to maintain system integrity against similar threats in the HFS subsystem and other kernel components.