CVE-2026-43366 in Linux
Summary
by MITRE • 05/08/2026
In the Linux kernel, the following vulnerability has been resolved:
io_uring/kbuf: check if target buffer list is still legacy on recycle
There's a gap between when the buffer was grabbed and when it potentially gets recycled, where if the list is empty, someone could've upgraded it to a ring provided type. This can happen if the request is forced via io-wq. The legacy recycling is missing checking if the buffer_list still exists, and if it's of the correct type. Add those checks.
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Analysis
by VulDB Data Team • 09/13/2026
The vulnerability identified in the Linux kernel's io_uring subsystem represents a critical race condition during buffer management operations that could potentially lead to system instability or privilege escalation. This issue specifically affects the kbuf component within io_uring which handles buffer recycling mechanisms for asynchronous I/O operations. The flaw manifests when buffer lists transition from legacy to ring-based structures during active I/O processing, creating a temporal window where improper buffer handling can occur.
The technical root cause stems from inadequate validation checks during buffer recycling operations within the io_uring subsystem. When a buffer is initially acquired and subsequently recycled, there exists a window of opportunity where the buffer list structure may have been modified by concurrent operations. This occurs particularly when requests are forcibly processed through the io-wq workqueue mechanism, which can trigger list upgrades from legacy to ring-based types. The legacy recycling code path fails to verify whether the target buffer list still exists in its original form and whether it maintains the expected legacy type structure.
This vulnerability operates under the principles of race condition exploitation as classified by CWE-362, where concurrent access to shared resources without proper synchronization leads to unpredictable behavior. The specific operational impact involves potential memory corruption and system instability when the recycling logic attempts to process buffers that have been modified by concurrent upgrade operations. The issue is particularly concerning because io_uring is designed for high-performance asynchronous I/O operations and is widely used in production systems, making the potential for exploitation significant.
The operational implications extend beyond simple system crashes to include potential privilege escalation scenarios where malicious actors could exploit this race condition to gain elevated system privileges. Attackers would need to carefully orchestrate concurrent operations that force the upgrade of buffer lists while simultaneously triggering the recycling process, creating a precise timing window for exploitation. This vulnerability affects systems running kernel versions where io_uring is actively utilized for asynchronous I/O operations, particularly in high-throughput environments where the io-wq workqueue mechanism is frequently engaged.
Mitigation strategies should focus on implementing proper validation checks before buffer recycling operations, ensuring that the buffer list type and existence are verified before proceeding with legacy recycling logic. The fix requires adding explicit checks to confirm that buffer lists have not been upgraded to ring-based structures and that they still maintain their expected legacy characteristics. System administrators should prioritize kernel updates that include this specific patch, as the vulnerability represents a fundamental flaw in the kernel's buffer management subsystem. Additionally, monitoring for concurrent io_uring operations and implementing proper synchronization primitives can help reduce the likelihood of exploitation in environments where the vulnerability may be present. The fix aligns with ATT&CK technique T1068 by addressing privilege escalation vectors through kernel-level buffer management flaws.