CVE-2026-98943 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
HID: steam: Clean up locking
This cleans up several issues with locking behavior, including RCU accesses not being guarded behind a lock.
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Analysis
by VulDB Data Team • 10/23/2026
The reported issue within the Linux kernel's HID subsystem for Steam devices highlights a critical concurrency flaw related to improper synchronization of Read-Copy-Update (RCU) data structures. In high-performance operating systems like Linux, RCU is frequently employed as a read-side optimization mechanism that allows multiple readers to access shared data concurrently without acquiring traditional mutexes or spinlocks, provided the writer ensures proper grace periods before freeing old versions of the data. However, this efficiency relies heavily on strict adherence to locking protocols during write operations and specific contexts where updates occur. The vulnerability arises when RCU accesses are performed in code paths that lack adequate protective locks, creating a race condition window where concurrent readers might dereference pointers that have been freed or modified by another thread. This scenario constitutes a classic use-after-free or data corruption vector, as the kernel may attempt to access memory regions that are no longer valid or contain stale information due to unsynchronized updates.
From a technical perspective, this flaw represents an improper synchronization mechanism where critical sections involving shared mutable state are not properly serialized. The absence of locking around RCU read-side accesses violates fundamental concurrency principles required for data integrity in multi-threaded environments. When the kernel processes input events from Steam peripherals, it may traverse linked lists or access configuration structures using RCU pointers without holding the necessary spinlocks that protect those structures during modification. If a writer thread updates these structures while a reader is mid-traversal due to missing locks, the reader could follow a dangling pointer leading to undefined behavior. This can manifest as kernel panics, system crashes, or subtle data corruption that compromises the stability of the input subsystem and potentially affects other parts of the operating system depending on how deeply the corrupted state propagates through memory management layers.
The operational impact of this vulnerability extends beyond simple instability for Steam device users. A successful exploitation could allow a local attacker with physical access to a USB HID interface or, in virtualized environments, a guest user interacting with emulated input devices to trigger these race conditions. By rapidly sending malformed or specifically timed input reports, an attacker might induce the kernel into accessing freed memory, potentially leading to arbitrary code execution if they can control the contents of the overwritten memory region. Even without full exploitation, the instability caused by such races results in denial-of-service conditions where the system becomes unresponsive or requires a hard reset due to kernel oopses triggered by invalid pointer dereferences within the interrupt handling paths for HID devices.
This vulnerability aligns with CWE-362, which describes concurrent execution using shared resources with improper synchronization, and specifically touches upon aspects of CWE-416 regarding use-after-free conditions resulting from race conditions in memory management. In terms of offensive security frameworks like MITRE ATT&CK, this flaw could be leveraged for Local Privilege Escalation if the attacker can escalate their privileges by exploiting the kernel memory corruption to gain control over execution flow or sensitive data structures within the ring 0 context. The remediation involves rigorous code review and refactoring of the HID Steam driver to ensure that all RCU read-side critical sections are correctly guarded with appropriate locking mechanisms where required, particularly in contexts where write-side updates might occur concurrently. Developers must implement proper spinlock protection around any access patterns that interact with data structures subject to concurrent modification, ensuring that the grace period semantics of RCU do not bypass necessary mutual exclusion requirements for safety-critical operations within the input subsystem.