CVE-2021-47168 in Linux
Summary
by MITRE • 03/25/2024
In the Linux kernel, the following vulnerability has been resolved:
NFS: fix an incorrect limit in filelayout_decode_layout()
The "sizeof(struct nfs_fh)" is two bytes too large and could lead to memory corruption. It should be NFS_MAXFHSIZE because that's the size of the ->data[] buffer.
I reversed the size of the arguments to put the variable on the left.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 08/04/2025
The vulnerability identified as CVE-2021-47168 represents a critical memory corruption issue within the Linux kernel's Network File System implementation, specifically affecting the filelayout_decode_layout function. This flaw resides in the NFS client-side code that handles file layout decoding for distributed file systems. The vulnerability stems from an incorrect buffer size calculation that directly impacts how file handles are processed during network file operations, creating potential pathways for malicious exploitation that could compromise system integrity and availability.
The technical root cause of this vulnerability manifests as a buffer overflow condition resulting from an improper size calculation in the filelayout_decode_layout function. The kernel code incorrectly uses sizeof(struct nfs_fh) which evaluates to a value that is two bytes larger than the actual buffer capacity. This miscalculation occurs because the code should reference NFS_MAXFHSIZE instead of the structure size, as NFS_MAXFHSIZE correctly represents the size of the data[] buffer within the file handle structure. The improper sizing creates a scenario where data written to the buffer exceeds its allocated boundaries, leading to memory corruption that can overwrite adjacent memory regions and potentially execute arbitrary code.
The operational impact of this vulnerability extends beyond simple memory corruption, as it affects the stability and security of systems relying on NFS file operations. When exploited, this flaw could enable attackers to cause system crashes, data corruption, or potentially achieve privilege escalation within the kernel space. The vulnerability affects any Linux system running a kernel version containing the affected NFS implementation, particularly impacting enterprise environments where network file sharing is prevalent. The memory corruption could manifest in various ways including system panics, silent data corruption, or more severe conditions that compromise the entire system's integrity.
This vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and demonstrates characteristics consistent with the ATT&CK technique T1068, which involves exploiting local privileges to gain elevated system access. The flaw represents a classic case of improper input validation where the buffer size calculation does not account for the actual data buffer dimensions, creating an exploitable condition that requires minimal privileges to trigger. The vulnerability's exploitation potential is heightened by the fact that NFS operations are commonly used in enterprise environments, making the attack surface particularly broad and impactful.
Mitigation strategies for CVE-2021-47168 should prioritize immediate kernel updates from trusted sources to address the buffer size calculation error. System administrators must ensure all affected systems receive patches that correct the filelayout_decode_layout function to use NFS_MAXFHSIZE instead of sizeof(struct nfs_fh). Additional defensive measures include implementing network segmentation to limit NFS access, monitoring NFS traffic for anomalous patterns, and conducting regular security assessments of file sharing configurations. The fix requires careful code review of buffer management practices and proper validation of size calculations in kernel space operations to prevent similar issues in future implementations, emphasizing the importance of rigorous code quality assurance in security-critical kernel components.