CVE-2023-53680 in Linux
Summary
by MITRE • 10/07/2025
In the Linux kernel, the following vulnerability has been resolved:
NFSD: Avoid calling OPDESC() with ops->opnum == OP_ILLEGAL
OPDESC() simply indexes into nfsd4_ops[] by the op's operation
number, without range checking that value. It assumes callers are careful to avoid calling it with an out-of-bounds opnum value.
nfsd4_decode_compound() is not so careful, and can invoke OPDESC() with opnum set to OP_ILLEGAL, which is 10044 -- well beyond the end of nfsd4_ops[].
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Analysis
by VulDB Data Team • 03/01/2026
The vulnerability identified as CVE-2023-53680 represents a critical buffer overflow condition within the Linux kernel's Network File System Daemon (NFSD) implementation. This flaw exists in the nfsd4_decode_compound() function which processes compound NFSv4 operations, specifically when handling operations with the illegal operation code OP_ILLEGAL. The issue stems from inadequate input validation and bounds checking mechanisms that allow the system to attempt indexing beyond the legitimate array boundaries of nfsd4_ops[]. The nfsd4_ops[] array contains the operational descriptors for all supported NFSv4 operations, but when OP_ILLEGAL is processed, the system attempts to access an index position of 10044 which far exceeds the actual array dimensions, creating a predictable memory access violation.
The technical implementation of this vulnerability occurs through the OPDESC() macro which serves as a lookup mechanism for NFSv4 operation descriptors by their operation number. This macro performs direct array indexing without implementing any range validation checks to ensure the operation number falls within acceptable bounds. When nfsd4_decode_compound() processes a compound operation that includes an illegal operation, it sets the operation number to OP_ILLEGAL which has a value of 10044, causing the macro to attempt accessing memory locations far beyond the allocated nfsd4_ops[] array. This direct memory access pattern violates fundamental security principles of array bounds checking and demonstrates a classic case of improper input validation. The vulnerability operates at the kernel level where such memory corruption can lead to arbitrary code execution or system instability.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to potentially enable privilege escalation and remote code execution attacks. An attacker capable of sending specially crafted NFSv4 compound operations to a vulnerable NFS server could exploit this flaw to overwrite critical kernel memory structures, potentially gaining elevated privileges or causing system crashes. The vulnerability affects all Linux kernel versions that implement the NFSv4 server functionality, making it particularly concerning for enterprise environments relying on NFS services. The attack vector is primarily through network-based NFS client connections, where malicious actors could leverage this flaw to compromise systems running vulnerable kernel versions. This vulnerability directly maps to CWE-129, which describes improper validation of array indices, and represents a clear violation of the principle of least privilege and input sanitization.
Mitigation strategies for CVE-2023-53680 should prioritize immediate patch application from kernel vendors, as the fix typically involves adding proper bounds checking to the OPDESC() macro or modifying nfsd4_decode_compound() to validate operation numbers before calling the descriptor lookup function. Organizations should also implement network segmentation to limit NFS service exposure and monitor for unusual NFS traffic patterns that might indicate exploitation attempts. The fix generally involves adding validation logic to ensure that operation numbers passed to OPDESC() are within the valid range of the nfsd4_ops[] array, preventing the out-of-bounds memory access that leads to the buffer overflow condition. Additionally, system administrators should consider implementing intrusion detection systems that can identify and alert on suspicious NFSv4 compound operation sequences that might indicate exploitation attempts. This vulnerability demonstrates the importance of robust input validation in kernel space operations and aligns with ATT&CK technique T1068, which covers local privilege escalation through kernel vulnerabilities.