CVE-2025-40324 in Linux
Summary
by MITRE • 12/08/2025
In the Linux kernel, the following vulnerability has been resolved:
NFSD: Fix crash in nfsd4_read_release()
When tracing is enabled, the trace_nfsd_read_done trace point crashes during the pynfs read.testNoFh test.
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Analysis
by VulDB Data Team • 02/23/2026
The vulnerability identified as CVE-2025-40324 represents a critical stability issue within the Linux kernel's network file system daemon implementation. This flaw manifests specifically within the nfsd4_read_release() function, which handles cleanup operations for NFS version 4 read operations. The issue occurs when kernel tracing mechanisms are actively enabled, creating a scenario where normal system operation can lead to unexpected kernel crashes. The vulnerability was discovered during testing of the pynfs test suite, specifically the read.testNoFh test case, which exercises NFS operations without proper file handle context. This particular test case triggers a race condition or invalid memory access pattern that causes the kernel to crash when attempting to process trace events related to NFS read operations.
The technical root cause of this vulnerability stems from improper handling of trace point events within the NFS daemon's cleanup path. When trace_nfsd_read_done is invoked during nfsd4_read_release(), the tracing subsystem attempts to access memory or data structures that may have already been freed or are in an inconsistent state. This represents a classic race condition scenario where the trace point execution overlaps with resource deallocation operations. The vulnerability falls under CWE-119 Improper Access to Memory Location, specifically manifesting as an out-of-bounds memory access or use-after-free condition. The crash occurs because the trace point infrastructure cannot properly handle the state of the NFS read operation when it is being released, particularly when the operation lacks proper file handle context as demonstrated by the failing test case.
The operational impact of CVE-2025-40324 extends beyond simple system crashes, as it affects the reliability and availability of NFS services within Linux environments. Systems running with kernel tracing enabled, such as those used for debugging, monitoring, or production environments with detailed logging requirements, become vulnerable to unexpected service disruptions. This vulnerability particularly affects enterprise storage infrastructures that rely on NFS for file sharing and can lead to cascading failures when NFS services become unavailable. The issue is exacerbated in environments where automated testing or continuous monitoring is performed, as the pynfs test suite represents common validation procedures that can trigger the crash. From an attacker perspective, this vulnerability could be exploited to cause denial of service against NFS services, potentially disrupting critical file sharing operations in server environments.
Mitigation strategies for CVE-2025-40324 should focus on both immediate patch application and operational security measures. The primary solution involves applying the kernel patch that resolves the race condition in trace point handling during NFS read operation cleanup. Organizations should prioritize updating their Linux kernel versions to include the fix for this vulnerability. In environments where immediate patching is not feasible, administrators can disable tracing capabilities for NFS operations when not actively debugging, thereby preventing the crash condition. Additionally, implementing monitoring systems that can detect and alert on NFS service disruptions can help maintain service availability. The vulnerability also highlights the importance of comprehensive testing for kernel subsystems, particularly those involving tracing and debugging mechanisms. Security teams should consider implementing automated testing procedures that include trace point validation to prevent similar issues from being introduced in future kernel versions. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 and T1566.001, representing denial of service through kernel-level instability and exploitation of system vulnerabilities for service disruption.