CVE-2026-89897 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
media: cec: Serialize exclusive follower delivery
cec_receive_notify() reads the exclusive follower pointer without the adapter lock. Serialize the no-follower check and message delivery against mode changes and release.
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Analysis
by VulDB Data Team • 09/16/2026
The identified vulnerability resides within the Linux kernel's Common Electronic Bus media subsystem, specifically affecting the Consumer Electronics Control or CEC protocol implementation. This component is responsible for managing communication between connected devices on a home entertainment bus, such as televisions, soundbars, and streaming players. The core issue stems from a race condition in the cec_receive_notify function, which handles incoming notifications and message deliveries to exclusive followers attached to a CEC adapter. In concurrent execution environments where multiple threads or interrupt handlers interact with the same adapter state, this lack of synchronization creates a window for data corruption and undefined behavior.
The technical flaw is characterized by an improper handling of shared resources without adequate locking mechanisms. Specifically, cec_receive_notify accesses the exclusive follower pointer to determine which device should receive a notification message. However, it performs this read operation outside the protection of the adapter lock. Simultaneously, other kernel routines responsible for changing the CEC mode or releasing the adapter can modify these same pointers and state variables concurrently. This absence of mutual exclusion means that one thread might be in the process of dereferencing a follower pointer while another thread is freeing memory associated with that follower or altering the operational mode of the adapter.
This race condition leads to significant operational impacts, primarily manifesting as kernel instability. If the exclusive follower pointer is accessed after it has been freed by a concurrent release operation, the system may attempt to dereference a dangling pointer. This typically results in an invalid memory access error, leading to a kernel panic or system crash. In less severe scenarios where the timing allows for partial data reads before modification, it could lead to corrupted message delivery, causing connected devices to misinterpret commands or fail to respond correctly. Such instability undermines the reliability of home automation and media control systems that depend on consistent CEC communication.
From a classification perspective, this vulnerability aligns with CWE-362, which describes concurrent execution using shared resources with an improper synchronization mechanism. The lack of atomicity in checking for followers and delivering messages allows for a classic time-of-check to time-of-use scenario where the state changes between verification and action. Furthermore, from a threat modeling standpoint such as MITRE ATT&CK, this type of race condition can be exploited by local attackers with user-level privileges to cause denial of service against the system or potentially escalate privileges if the resulting memory corruption allows for arbitrary code execution through heap exploitation techniques.
To mitigate this vulnerability, it is essential to enforce strict serialization around all accesses to the exclusive follower pointer and related state variables within the CEC adapter structure. The fix involves wrapping the no-follower check and subsequent message delivery logic inside a critical section protected by the adapter lock. This ensures that mode changes and release operations are serialized against notification deliveries, preventing concurrent modification of shared data structures. System administrators should apply kernel updates provided by their distribution vendors as soon as they become available to patch this synchronization flaw. Additionally, developers working on similar subsystems should audit other areas where hardware state is accessed without proper locking to prevent analogous race conditions in future code revisions.