CVE-2026-68334 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
rxrpc: fix io_thread race in rxrpc_wake_up_io_thread()
rxrpc_wake_up_io_thread() checks local->io_thread before waking it, but then reloads the pointer for wake_up_process().
local->io_thread is cleared with WRITE_ONCE() when the I/O thread exits, so the second load can see NULL even if the first load did not.
Take a READ_ONCE() snapshot and use it for both the NULL check and the wake_up_process() call, as rxrpc_encap_rcv() already does.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability in question affects the Linux kernel's rxrpc subsystem, specifically within the rxrpc_wake_up_io_thread() function where a race condition can occur during I/O thread management. This issue represents a classic concurrency problem where multiple threads access shared memory locations without proper synchronization mechanisms. The flaw manifests when the function performs a check on local->io_thread before proceeding to wake up the process, but fails to maintain consistency between the initial pointer read and subsequent usage. The race condition emerges because while the io_thread pointer is cleared using WRITE_ONCE() during thread exit, a second load of the same pointer can return NULL even if the first load returned a valid thread reference.
The technical implementation of this vulnerability stems from improper handling of concurrent access patterns within the kernel's networking subsystem. The rxrpc subsystem manages remote execution RPC calls over various transport protocols and requires careful coordination between different kernel threads to process incoming data packets effectively. When rxrpc_encap_rcv() processes encapsulated received data, it already implements proper protection by using READ_ONCE() snapshots for consistent pointer access. However, the wake_up_io_thread() function lacks this same protective mechanism, creating a window where a thread might be woken up with a NULL pointer reference or alternatively, the check might pass when it should have failed.
This race condition has significant operational implications for systems relying on Linux kernel networking functionality and particularly those utilizing remote procedure call mechanisms. The vulnerability could lead to system instability through null pointer dereferences or process wake-up failures that disrupt normal network communication patterns. Depending on the system configuration and workload, such issues may manifest as intermittent service disruptions or more severe system crashes, potentially affecting critical infrastructure components that depend on reliable RPC communication. The impact extends beyond simple performance degradation to potential security implications where improper thread management could create unexpected access patterns.
The recommended mitigation involves implementing consistent pointer access patterns throughout the subsystem by adopting the same approach already used in rxrpc_encap_rcv(). This requires taking a READ_ONCE() snapshot of the io_thread pointer before performing any operations that depend on its value, ensuring that both the NULL check and the wake_up_process() call operate on identical pointer values. This approach aligns with established kernel development practices for handling concurrent access to shared data structures and follows the principles outlined in CWE-362 which addresses race conditions in concurrent programming. The fix should be applied across all similar functions within the rxrpc subsystem that handle thread management operations, ensuring consistent behavior and eliminating potential attack vectors through improper synchronization.
From an ATT&CK perspective, this vulnerability could enable privilege escalation or denial of service attacks if exploited by malicious actors who understand kernel concurrency patterns. The fix addresses a fundamental race condition that could be leveraged in advanced persistent threat scenarios where attackers seek to destabilize system networking components. Organizations should prioritize applying this patch to systems running affected kernel versions and monitor for any unusual network behavior following the update, particularly in environments where high availability and reliable RPC communication are critical requirements.