CVE-2026-74661 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
mac802154: fix netdev use-after-free in beacon worker
mac802154_beacon_worker() reads local->beacon_req under RCU and derives the sub-interface from the request, but then drops the RCU read lock and continues to use both sdata and the embedded wpan_dev.
mac802154_stop_beacons_locked() cancels only pending beacon work, clears local->beacon_req and frees the request. A beacon worker that is already running can therefore continue after interface teardown and dereference the freed netdev private area.
The scan worker already pins the netdev before leaving RCU. Apply the same lifetime rule to the beacon worker: take a netdev reference while the request is still protected by RCU, and release it on all paths that continue after the reference is acquired.
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Analysis
by VulDB Data Team • 08/22/2026
The vulnerability identified in the Linux kernel within the mac802154 subsystem represents a critical use-after-free condition affecting network device management during beacon processing operations. This flaw originates from an improper handling of Reference Counting and Read-Copy-Update (RCU) synchronization primitives, which are fundamental mechanisms for ensuring thread safety and memory integrity in concurrent environments. The core issue resides within the mac80214_beacon_worker function, which is responsible for managing beacon transmission schedules for IEEE 802.15.4 wireless networks. During its execution, this worker routine accesses local->beacon_req under an RCU read lock to safely retrieve data structures without blocking other threads. However, the implementation fails to maintain proper object lifetime guarantees after exiting the critical section defined by the RCU lock.
Specifically, the code derives a pointer to the sub-interface structure and its embedded wireless device context from the beacon request while still within the protected region. Once the function proceeds past this point, it releases the RCU read lock but continues to dereference these pointers in subsequent operations. This creates a race condition window where another thread can trigger interface teardown procedures that dismantle the network device infrastructure. When mac802154_stop_beacons_locked is invoked during such teardown sequences, it cancels pending beacon work items and frees the memory associated with local->beacon_req. Consequently, if a beacon worker instance was already executing when this cleanup occurred, it will proceed to access memory that has been deallocated by the system, leading to undefined behavior, potential kernel panics, or arbitrary code execution depending on how the freed memory is subsequently utilized and overwritten by other allocations.
The operational impact of this vulnerability extends beyond simple stability issues. A successful exploitation could allow a local attacker with network interface privileges to crash the host system, resulting in a denial-of-service condition that disrupts all network services running on the affected machine. In more sophisticated scenarios, if an attacker can control the contents written into the freed memory region through carefully crafted allocation patterns, they might achieve arbitrary code execution within the kernel space, thereby gaining full control over the operating system and bypassing user-space security boundaries entirely. This aligns with CWE-416, which classifies use-after-free errors as a significant category of software defects that compromise memory safety integrity.
From an offensive security perspective, this vulnerability maps to ATT&CK technique T1059, specifically command or script interpretation within the context of local privilege escalation via kernel exploitation. The lack of proper reference counting allows for time-of-check-to-time-of-use (TOCTOU) scenarios where the state of the object changes between validation and usage. To mitigate this risk, developers must enforce strict lifetime management rules consistent with established patterns in similar subsystems such as the scan worker implementation. The corrective action involves acquiring a net device reference count while the beacon request is still protected by the RCU read lock. This ensures that the network device structure remains valid for the duration of the beacon worker's execution, regardless of concurrent teardown operations.
The fix requires releasing this acquired reference on all code paths where the function continues after securing it, thereby balancing the reference counts and preventing premature deallocation. By adopting this approach, the kernel guarantees that the underlying data structures persist until they are no longer needed by active workers. This change reinforces the principle of explicit ownership transfer in concurrent programming models. System administrators should apply available kernel updates promptly to patch this flaw, as unpatched systems remain vulnerable to local privilege escalation attacks targeting network subsystems. Regular auditing of RCU usage patterns and adherence to reference counting best practices are essential for maintaining long-term system resilience against memory corruption vulnerabilities.