Source: cve@mitre.org
Certain NFS servers allow users to use mknod to gain privileges by creating a writable kmem device and setting the UID to 0.
Critical vulnerability in certain NFS servers allows attackers to achieve root privileges by exploiting a flaw in how the server handles the mknod system call. Successful exploitation grants complete control over the compromised system, leading to data breaches and system compromise.
Step 1: NFS Mount: The attacker establishes an NFS mount to the vulnerable server. This requires network access to the server and the NFS share being exported.
Step 2: mknod Creation: The attacker uses the mknod system call to create a special file (character device) within the mounted NFS share. The attacker attempts to create a device file that maps to kernel memory, such as /dev/kmem (or a similar device depending on the OS). The attacker specifies the device type and major/minor numbers to correspond to the target device.
Step 3: Ownership Manipulation: The attacker uses the chown system call to change the ownership of the newly created device file to root (UID 0). This step is crucial for gaining elevated privileges.
Step 4: Kernel Memory Access: The attacker now has read/write access to kernel memory through the created device file. They can then read and write to kernel memory, potentially leading to arbitrary code execution or system compromise.
Step 5: Privilege Escalation: The attacker leverages the kernel memory access to execute arbitrary code with kernel privileges. This could involve modifying kernel data structures, injecting malicious code, or exploiting other kernel vulnerabilities.
The vulnerability stems from a lack of proper access control and validation within the NFS server's handling of the mknod system call. Specifically, the server fails to adequately restrict the creation of special files (like character devices) within the exported file system. An attacker can leverage this to create a writable device file, such as /dev/kmem, and then manipulate its ownership to root (UID 0). This allows the attacker to read and write to kernel memory, enabling them to execute arbitrary code with kernel privileges. The root cause is a missing or inadequate check on the user's ability to create special files with specific attributes, combined with a failure to properly sanitize user-supplied data before interacting with the kernel's device drivers. This is a classic privilege escalation vulnerability.
This vulnerability is not directly associated with specific APT groups due to its age. However, any attacker with network access and knowledge of the vulnerability could exploit it. The potential impact of this vulnerability is significant, as it can lead to complete system compromise. CISA KEV: Not Listed due to the age of the vulnerability.
Monitor NFS server logs for suspicious mknod and chown system calls, especially those targeting device files.
Analyze network traffic for NFS mount requests and subsequent file creation activity.
Implement file integrity monitoring to detect unauthorized changes to critical system files, including device files.
Use intrusion detection systems (IDS) with rules specifically designed to detect exploitation attempts against NFS servers.
Review system logs for unusual access to /dev/kmem or similar kernel memory devices.
Look for the creation of special files (character or block devices) within NFS shares.
Disable NFS if not required. If NFS is required, restrict access to trusted clients only.
Upgrade or patch the NFS server software to the latest version. Ensure that the server has implemented the necessary security fixes to address this vulnerability.
Implement strong access controls on NFS shares, limiting the ability of users to create special files.
Regularly audit NFS server configurations to ensure that they are secure and up-to-date.
Use a file system that supports fine-grained access control to restrict the creation of special files.
Implement a host-based intrusion detection system (HIDS) to monitor for suspicious activity on the server.