CVE-2013-4591 in Linux
Summary
by MITRE
Buffer overflow in the __nfs4_get_acl_uncached function in fs/nfs/nfs4proc.c in the Linux kernel before 3.7.2 allows local users to cause a denial of service (memory corruption and system crash) or possibly have unspecified other impact via a getxattr system call for the system.nfs4_acl extended attribute of a pathname on an NFSv4 filesystem.
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Analysis
by VulDB Data Team • 06/02/2021
The vulnerability described in CVE-2013-4591 represents a critical buffer overflow flaw within the Linux kernel's NFSv4 implementation that affects systems running kernel versions prior to 3.7.2. This issue resides in the __nfs4_get_acl_uncached function located in fs/nfs/nfs4proc.c, which handles the retrieval of access control lists for NFSv4 filesystems when cached data is unavailable. The flaw manifests when a local user executes a getxattr system call targeting the system.nfs4_acl extended attribute of any pathname on an NFSv4 mounted filesystem, creating a condition where insufficient input validation leads to memory corruption.
The technical nature of this vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions where insufficient bounds checking allows attackers to write beyond allocated memory boundaries. The flaw occurs during the processing of extended attributes in the NFSv4 protocol implementation, specifically when handling the system.nfs4_acl attribute that stores access control information. The buffer overflow vulnerability stems from inadequate validation of the extended attribute name length and the subsequent processing of the ACL data structure without proper boundary checks, allowing malicious input to overwrite adjacent memory regions.
Operationally, this vulnerability presents significant risks to system stability and security as it can be exploited by local users to trigger system crashes through memory corruption, resulting in denial of service conditions that may require system reboot to recover. The potential impact extends beyond simple denial of service, as the memory corruption could potentially be leveraged to execute arbitrary code with kernel privileges, though the exact exploitability remains unspecified in the original report. The vulnerability affects systems where NFSv4 filesystems are mounted and accessed locally, making it particularly concerning for servers and workstations that rely on network file sharing protocols. The exploit requires local access to the system but does not require network connectivity, making it a latent threat that can be activated by any user with access to the affected system.
Mitigation strategies for this vulnerability primarily involve upgrading to Linux kernel versions 3.7.2 or later where the buffer overflow has been addressed through proper bounds checking and input validation. System administrators should prioritize patching affected systems and monitor for any signs of exploitation attempts. Additionally, implementing network segmentation and access controls can help limit local user access to potentially vulnerable systems. The vulnerability demonstrates the importance of proper input validation in kernel space operations and highlights the need for comprehensive security testing of filesystem implementations. Organizations should also consider implementing intrusion detection systems to monitor for unusual getxattr system call patterns that might indicate exploitation attempts. This vulnerability serves as a reminder of the critical security implications of kernel-level buffer overflows and the necessity of maintaining up-to-date system software to protect against known vulnerabilities. The flaw underscores the relationship between the ATT&CK technique T1068, which involves exploiting local privileges, and the broader category of kernel exploitation techniques that can lead to privilege escalation and system compromise.