CVE-2025-40047 in Linux
Summary
by MITRE • 10/28/2025
In the Linux kernel, the following vulnerability has been resolved:
io_uring/waitid: always prune wait queue entry in io_waitid_wait()
For a successful return, always remove our entry from the wait queue entry list. Previously this was skipped if a cancelation was in progress, but this can race with another invocation of the wait queue entry callback.
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Analysis
by VulDB Data Team • 05/20/2026
The vulnerability identified as CVE-2025-40047 resides within the Linux kernel's io_uring subsystem, specifically addressing a race condition in the waitid implementation that could lead to resource management issues and potential system instability. This flaw affects the io_waitid_wait() function which handles process waiting operations within the io_uring framework, a high-performance asynchronous I/O interface designed to provide efficient I/O operations for applications. The issue stems from improper handling of wait queue entries during concurrent operations, creating a scenario where cleanup operations may be skipped under specific conditions.
The technical flaw manifests when the io_waitid_wait() function processes wait queue entries for process monitoring operations. Under normal circumstances, the function should always remove its entry from the wait queue list upon successful completion of the wait operation. However, the previous implementation contained a logic error where the cleanup operation was conditionally skipped when a cancellation was in progress. This conditional behavior created a race condition that could occur between the cancellation process and subsequent invocations of the wait queue entry callback. The race condition arises because the system attempts to manage concurrent access to shared data structures without proper synchronization, leading to potential memory leaks or corrupted data structures.
From an operational perspective, this vulnerability could result in several security and stability concerns within Linux systems utilizing io_uring for asynchronous I/O operations. The improper cleanup of wait queue entries may lead to memory exhaustion over time, as stale entries accumulate in the system's data structures. This accumulation could degrade system performance and potentially lead to system crashes or denial of service conditions. The vulnerability affects systems where applications rely heavily on io_uring's waitid functionality for process monitoring, which is common in high-performance applications such as web servers, database systems, and network services that require efficient I/O handling and process management capabilities.
The mitigation for this vulnerability involves updating to a patched version of the Linux kernel where the io_waitid_wait() function has been corrected to always prune wait queue entries regardless of cancellation status. System administrators should prioritize applying these kernel updates, particularly in production environments where io_uring is actively used. The fix aligns with security best practices for concurrent programming and proper resource management, ensuring that all allocated resources are properly released even under race conditions. This correction addresses a fundamental flaw in the kernel's process waiting mechanism and demonstrates the importance of robust synchronization in kernel-level code. The vulnerability's resolution follows established security principles and addresses potential issues that could be exploited to cause system instability or resource exhaustion, making it a critical update for maintaining system integrity and performance.
This vulnerability type corresponds to CWE-362, which describes a race condition in concurrent programming, and aligns with ATT&CK technique T1499.001, which covers resource exhaustion and denial of service conditions. The fix represents a standard approach to addressing race conditions in kernel code, ensuring proper cleanup operations even under concurrent access scenarios. The issue demonstrates the critical importance of thorough testing and validation of concurrent code paths in operating system kernels, where race conditions can have severe implications for system stability and security.