CVE-2009-1336 in Linux
Summary
by MITRE
fs/nfs/client.c in the Linux kernel before 2.6.23 does not properly initialize a certain structure member that stores the maximum NFS filename length, which allows local users to cause a denial of service (OOPS) via a long filename, related to the encode_lookup function.
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Analysis
by VulDB Data Team • 09/02/2019
The vulnerability identified as CVE-2009-1336 resides within the Linux kernel's Network File System implementation, specifically in the fs/nfs/client.c file. This flaw represents a classic case of improper initialization that can lead to system instability and denial of service conditions. The vulnerability affects Linux kernel versions prior to 2.6.23, making it a significant concern for systems running older kernel versions that have not received the necessary security patches.
The technical root cause of this vulnerability stems from the improper initialization of a structure member responsible for storing the maximum NFS filename length. When the encode_lookup function processes filenames, it relies on this uninitialized variable to determine buffer boundaries for filename handling. This initialization failure creates a scenario where the system uses unpredictable or arbitrary values for the maximum filename length, leading to potential buffer overflows or memory corruption when handling long filenames. The vulnerability is particularly concerning because it operates at the kernel level, where such flaws can have cascading effects on system stability and security.
The operational impact of CVE-2009-1336 manifests as a local denial of service condition, commonly resulting in kernel oops messages and system instability. An attacker with local access can exploit this vulnerability by creating or accessing files with exceptionally long filenames that exceed the bounds of the uninitialized buffer. This type of attack falls under the category of privilege escalation and denial of service, as it allows local users to disrupt system operations without requiring elevated privileges. The vulnerability aligns with CWE-457, which addresses the use of uninitialized variables, and demonstrates how such issues can translate into practical security exploits in kernel space.
From an attack perspective, this vulnerability is classified as a local privilege escalation vector that can be exploited by any user with access to the system. The exploit requires minimal privileges and can be executed through simple file operations involving long filenames. The ATT&CK framework categorizes this under privilege escalation techniques, specifically leveraging kernel-level flaws to gain unauthorized system access or cause service disruption. Organizations should note that this vulnerability represents a classic example of how seemingly minor initialization errors in kernel code can have significant security implications, particularly when dealing with network filesystem implementations that handle user-provided data.
The recommended mitigations for CVE-2009-1336 involve upgrading to Linux kernel version 2.6.23 or later, where the initialization issue has been properly addressed. System administrators should implement comprehensive patch management procedures to ensure all affected systems receive the necessary kernel updates. Additionally, monitoring for unusual system behavior, particularly kernel oops messages or unexpected system crashes, can help detect exploitation attempts. Organizations should also consider implementing access controls to limit local user privileges where possible, as this vulnerability can be exploited by any local user with file system access. The fix implemented in kernel 2.6.23 properly initializes the structure member, preventing the use of uninitialized values that could lead to memory corruption and system instability.