CVE-2009-3726 in Linux
Summary
by MITRE
The nfs4_proc_lock function in fs/nfs/nfs4proc.c in the NFSv4 client in the Linux kernel before 2.6.31-rc4 allows remote NFS servers to cause a denial of service (NULL pointer dereference and panic) by sending a certain response containing incorrect file attributes, which trigger attempted use of an open file that lacks NFSv4 state.
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Analysis
by VulDB Data Team • 12/08/2024
The vulnerability described in CVE-2009-3726 represents a critical denial of service flaw within the Linux kernel's Network File System version 4 implementation. This issue specifically affects the nfs4_proc_lock function located in the fs/nfs/nfs4proc.c file, which handles locking operations in NFSv4 client environments. The vulnerability arises from insufficient input validation when processing responses from NFS servers, creating a condition where malicious or malformed server responses can trigger system instability. The flaw operates by exploiting a NULL pointer dereference scenario that ultimately results in kernel panic, effectively rendering the affected system unavailable to provide file services. This type of vulnerability falls under the category of improper input validation as classified by CWE-20, specifically manifesting as a NULL pointer dereference issue that can be leveraged to cause system crashes.
The technical exploitation of this vulnerability occurs when an NFS server sends a specially crafted response containing incorrect file attributes to a Linux client system running an affected kernel version. During the processing of these malformed responses, the nfs4_proc_lock function attempts to access file state information that has not been properly initialized or validated, leading to the NULL pointer dereference. The lack of proper state validation in the NFSv4 client implementation means that when the system encounters an open file without proper NFSv4 state information, it fails to handle this condition gracefully and instead crashes the kernel. This behavior represents a classic example of inadequate error handling in kernel space code, where the absence of proper null checks and state validation creates a path to system termination.
From an operational perspective, this vulnerability poses significant risks to systems relying on NFSv4 for file sharing and storage services. Any system running a Linux kernel version prior to 2.6.31-rc4 that connects to untrusted or potentially compromised NFS servers becomes vulnerable to this attack vector. The impact extends beyond simple service disruption as the kernel panic can result in complete system unavailability, requiring manual reboot and potentially leading to data loss if the system was in the middle of critical operations. Organizations using NFSv4 services, particularly in enterprise environments where file sharing is fundamental to operations, face potential business disruption and increased operational overhead due to the need for immediate patching and system restarts. The vulnerability can be exploited remotely through network-based attacks, making it particularly dangerous in environments where systems are exposed to untrusted network traffic.
The mitigation strategy for CVE-2009-3726 centers on upgrading to kernel versions 2.6.31-rc4 or later, where the vulnerability has been addressed through improved input validation and proper state handling in the NFSv4 client implementation. System administrators should prioritize patching affected systems, particularly those that maintain connections to external NFS servers or operate in environments where network traffic cannot be fully trusted. Additional defensive measures include implementing network segmentation to limit NFS server access to trusted systems, using firewall rules to restrict NFS traffic, and monitoring for unusual network activity that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper kernel security practices and input validation in maintaining system stability. From an ATT&CK framework perspective, this vulnerability aligns with techniques related to privilege escalation and denial of service, specifically targeting the kernel level through improper input handling. Organizations should also consider implementing intrusion detection systems that can identify patterns associated with NFS protocol anomalies that might indicate exploitation attempts. The remediation process requires careful planning due to the potential for system downtime during patch deployment, particularly in mission-critical environments where immediate availability is essential.