CVE-2009-0269 in Linux
Summary
by MITRE
fs/ecryptfs/inode.c in the eCryptfs subsystem in the Linux kernel before 2.6.28.1 allows local users to cause a denial of service (fault or memory corruption), or possibly have unspecified other impact, via a readlink call that results in an error, leading to use of a -1 return value as an array index.
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Analysis
by VulDB Data Team • 08/28/2019
The vulnerability described in CVE-2009-0269 resides within the eCryptfs subsystem of the Linux kernel, specifically in the fs/ecryptfs/inode.c file. This flaw represents a classic buffer overflow condition that can be exploited through improper error handling mechanisms. The eCryptfs filesystem implementation provides transparent encryption for files and directories, making it a critical component in Linux security infrastructure. When a readlink system call is executed against an eCryptfs filesystem, the kernel processes this operation through the inode.c module where the vulnerability manifests.
The technical flaw occurs when an error condition is encountered during a readlink operation on an eCryptfs filesystem. Under normal circumstances, the kernel should handle such errors gracefully and prevent further processing. However, in this case, when an error occurs, the system returns a -1 value from the error handling routine, which is then subsequently used as an array index in the subsequent code execution path. This represents a fundamental violation of input validation principles and demonstrates poor error handling practices. The use of a negative integer as an array index creates undefined behavior that can result in either kernel crashes or memory corruption, depending on the specific execution context.
The operational impact of this vulnerability extends beyond simple denial of service conditions. While local users can trigger a kernel fault that results in system instability, the more concerning aspect involves potential memory corruption that could be exploited for privilege escalation or other malicious activities. The vulnerability affects Linux kernel versions prior to 2.6.28.1, representing a significant window of exposure for systems running older kernel versions. This flaw aligns with CWE-129, which addresses improper validation of array indices, and demonstrates how seemingly minor error handling oversights can create substantial security risks. The vulnerability also maps to ATT&CK technique T1068, which involves exploiting local privileges to gain system-level access through kernel vulnerabilities.
The exploitation of this vulnerability requires local user access and involves crafting specific readlink calls against eCryptfs filesystems. However, the implications are severe as it allows for both system stability compromise and potential privilege escalation. The memory corruption aspect suggests that an attacker could potentially manipulate kernel memory structures, though the exact exploitability for arbitrary code execution remains dependent on various system configurations and memory layouts. This vulnerability highlights the importance of robust error handling in kernel space code and demonstrates why comprehensive security testing of kernel subsystems is essential. The fix implemented in kernel version 2.6.28.1 involved proper validation of return values before using them as array indices, addressing the root cause of the vulnerability through defensive programming practices.
Systems administrators should prioritize upgrading to kernel versions 2.6.28.1 or later to mitigate this vulnerability. Organizations running older kernel versions should conduct immediate vulnerability assessments and implement monitoring for potential exploitation attempts. The vulnerability serves as a reminder of the critical nature of kernel security and the potential for seemingly benign error conditions to create severe system instability. This flaw underscores the necessity of thorough code review processes for kernel subsystems and the importance of adhering to security best practices in low-level system programming. The impact extends to enterprise environments where eCryptfs is actively deployed, making this vulnerability particularly significant for organizations maintaining Linux-based security infrastructures.