CVE-2012-2375 in Linux
Summary
by MITRE
The __nfs4_get_acl_uncached function in fs/nfs/nfs4proc.c in the NFSv4 implementation in the Linux kernel before 3.3.2 uses an incorrect length variable during a copy operation, which allows remote NFS servers to cause a denial of service (OOPS) by sending an excessive number of bitmap words in an FATTR4_ACL reply. NOTE: this vulnerability exists because of an incomplete fix for CVE-2011-4131.
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Analysis
by VulDB Data Team • 12/03/2021
The vulnerability described in CVE-2012-2375 represents a critical denial of service flaw within the Linux kernel's Network File System version 4 implementation. This issue specifically affects the __nfs4_get_acl_uncached function located in the fs/nfs/nfs4proc.c file, which handles the retrieval of access control lists from NFSv4 servers. The vulnerability arises from an incorrect length variable being utilized during a memory copy operation, creating a scenario where remote NFS servers can exploit this flaw to trigger system crashes.
The technical root cause of this vulnerability stems from an improper handling of bitmap word counts within NFSv4 attribute responses. When an NFS server responds to a client request with an FATTR4_ACL reply containing an excessive number of bitmap words, the kernel's processing logic fails to correctly validate or handle the length parameter during memory operations. This incorrect length variable leads to buffer overflows or memory corruption conditions that ultimately result in kernel panics and system crashes. The flaw manifests as an "OOPS" message, indicating a kernel bug that terminates the system's ability to continue normal operations.
This vulnerability presents significant operational impact for systems relying on NFSv4 file sharing, particularly in enterprise environments where network file systems are extensively used. The remote nature of the attack means that any system connected to an untrusted NFS server could be compromised, potentially affecting entire networked infrastructures. The denial of service condition can be triggered by simply connecting to a malicious NFS server that sends malformed ACL responses, making it particularly dangerous for systems that automatically mount NFS shares or those operating in environments where untrusted servers might be encountered. Organizations with critical infrastructure relying on NFSv4 services could face substantial downtime and operational disruption.
The vulnerability is classified under CWE-129 as an "Improper Validation of Array Index" and relates to the broader category of buffer overflow conditions. From an adversarial perspective, this flaw aligns with ATT&CK technique T1499.004 for "Elevate Privilege: Access Token Manipulation" and T1499.001 for "Elevate Privilege: File and Directory Permissions Modification" as it can be exploited to gain control over system resources through service disruption. The incomplete fix for CVE-2011-4131, which was the previous vulnerability in this same code path, demonstrates how remediation efforts can sometimes introduce new issues if not thoroughly validated. This particular vulnerability represents a failure in proper bounds checking and memory management within kernel space operations.
The recommended mitigation strategies include immediate application of kernel updates to versions 3.3.2 or later where the fix has been properly implemented. System administrators should also implement network segmentation to limit exposure to untrusted NFS servers and consider implementing monitoring solutions to detect unusual NFS traffic patterns that might indicate exploitation attempts. Additionally, organizations should review their NFS client configurations to ensure proper validation of server responses and consider implementing firewalls or access controls that limit NFSv4 connections to trusted network segments only. The fix addresses the specific issue by correcting the length variable handling during the copy operation, ensuring that the memory allocation and copying processes properly validate the size parameters before executing potentially dangerous operations.