CVE-2026-98750 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
tty: fix saved termios reset race
Resetting saved termios state on device registration is needed where a minor number can be reused for an entirely different device and where the old settings may prevent the port from even being opened (e.g. when CLOCAL is not set).
Not all TTY drivers guarantee that the minor number is no longer in use when registering devices however, something which can lead to a use-after-free when closing a TTY (and saving its termios) races with re-registration.
Add a new TTY_DRIVER_RESET_SAVED_TERMIOS flag to request that any saved termios state is reset on registration and only set it for drivers that make sure that the minor number is no longer in use.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel's terminal subsystem contains a critical race condition related to the management of serial line settings, specifically involving the saving and resetting of termios structures during device lifecycle events. This vulnerability arises from an inconsistency in how different TTY drivers handle minor number reuse when devices are registered or unregistered. In many embedded systems and virtualized environments, hardware resources such as UART ports may be dynamically allocated or reused across different physical or logical interfaces. When a terminal interface is closed, the kernel saves its current termios state to preserve configuration settings for potential future use. However, if that same minor number is subsequently assigned to an entirely new device before the previous session's cleanup completes, the saved termios data may still be associated with the old context. This creates a scenario where stale or invalid terminal configurations are applied to a different hardware entity, potentially preventing the port from being opened correctly due to restrictive flags such as CLOCAL not being set, which dictates whether carrier detection is required for opening the device.
The core technical flaw lies in the lack of synchronization between driver registration and termios state management across varying TTY implementations. Not all kernel drivers guarantee that a minor number is completely released and cleared before it can be reassigned to another device instance. Consequently, when one session closes and saves its terminal settings while another process attempts to register or open a new device using the same minor number, a race condition occurs. This asynchronous behavior leads to use-after-free vulnerabilities because the kernel may attempt to access memory structures associated with the old termios state that have already been freed by the previous driver instance. The absence of a standardized mechanism to ensure atomicity in resetting these saved states allows malicious actors or buggy applications to exploit this timing window, potentially leading to kernel crashes, privilege escalation through arbitrary code execution via corrupted pointers, or denial of service conditions where legitimate users cannot access terminal devices due to misconfigured state inheritance.
From an industry standards perspective, this vulnerability maps directly to CWE-416 Use After Free and CWE-362 Concurrent Execution Using Shared Resource with Improper Synchronization Race Condition. The failure to properly synchronize the release of resources with their reuse constitutes a classic concurrency error that undermines system integrity. Furthermore, within the MITRE ATT&CK framework for enterprise security, this type of kernel-level race condition can be leveraged in techniques related to Privilege Escalation via TTY devices or Defense Evasion through process injection if an attacker gains initial foothold on the terminal subsystem. The exploitation vector typically involves rapid opening and closing of serial ports combined with concurrent device registration attempts, requiring local access but potentially yielding significant control over the host system depending on the privileges of the invoking user space processes.
To mitigate this risk, kernel developers have introduced a new flag named TTY_DRIVER_RESET_SAVED_TERMIOS which must be explicitly set by drivers that can guarantee minor number reuse safety. This flag instructs the terminal layer to forcibly reset any saved termios state upon device registration, ensuring that stale configurations from previous sessions do not interfere with newly registered devices. Drivers that cannot make this guarantee should avoid setting the flag and instead rely on stricter resource management practices or patch their internal logic to prevent minor number reuse until all associated resources are fully released. System administrators and developers maintaining custom TTY drivers must audit their implementations to ensure they either adopt this new flag where appropriate or implement robust locking mechanisms around termios save and restore operations. Updating the Linux kernel to a version that includes this fix is essential for environments relying on dynamic serial port allocation, particularly in IoT devices, industrial control systems, and cloud infrastructure instances where resource reuse patterns are common and security boundaries must remain strict against local exploitation attempts.