CVE-2026-98752 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
tty: port: fix tty_port_tty_vhangup() race
Drivers rely on tty_port_tty_vhangup() to synchronously hang up their ports before tearing down resources as part of deregistration (e.g. on physical disconnect).
If tty_port_tty_vhangup() races with another hangup it may however return before the port has been shut down. This is in turn can lead to use-after-free and NULL-pointer dereferences in racing ioctls (including a synchronous hangup) and in processing of racing asynchronous hangups (carrier loss).
Add the missing serialisation to tty_port_tty_vhangup() and tty_port_hangup() so that the former does not return until the port has been shut down also when there is a racing hangup.
Note that serial core does not use tty_port_hangup(), but it already holds the port mutex when clearing port->tty and shutting down the port in uart_hangup().
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel's TTY subsystem manages terminal devices, providing an abstraction layer for character-oriented input and output. A critical race condition was identified within the tty_port_tty_vhangup() function, which is responsible for synchronously hanging up a serial port before resources are torn down during driver deregistration or physical disconnection events. The core issue arises when this function races with another concurrent hangup operation, such as one triggered by carrier loss or an explicit ioctl call. In such scenarios, the function may return prematurely, indicating completion of the hangup process even though the underlying port has not yet been fully shut down. This premature return creates a window where subsequent operations can interact with resources that are in an inconsistent state, leading to severe stability and security issues including use-after-free conditions and NULL-pointer dereferences.
From a technical perspective, the vulnerability stems from insufficient serialization within the TTY port management logic. When multiple hangup requests occur simultaneously, the lack of proper locking mechanisms allows one request to proceed while another is still in progress but not yet finalized. This race condition violates the expected atomicity of resource cleanup operations. Specifically, asynchronous hangups resulting from carrier loss and synchronous hangups initiated via ioctls can interleave with the deregistration process. The absence of a mutex or similar synchronization primitive around the critical section where port state is modified allows these concurrent threads to access shared data structures without mutual exclusion. This leads to scenarios where memory associated with the TTY structure might be freed while still being referenced by other active processes, resulting in undefined behavior that can crash the system or potentially allow for privilege escalation if exploited carefully.
The operational impact of this vulnerability is significant, affecting systems relying on serial communication and virtual terminal interfaces. Use-after-free vulnerabilities are particularly dangerous as they can lead to arbitrary code execution under certain conditions, while NULL-pointer dereferences typically result in kernel panics and denial of service. For environments where hardware connectivity changes frequently or where multiple processes manage TTY devices concurrently, this race condition poses a persistent risk. The vulnerability affects the integrity of the kernel's device management layer, potentially compromising system stability and security posture. Attackers with local access could exploit these races to destabilize the operating system or escalate privileges by manipulating the timing of hangup operations relative to resource deallocation.
To mitigate this issue, the Linux kernel developers have implemented additional serialization within tty_port_tty_vhangup() and tty_port_hangup(). The fix ensures that tty_port_tty_vhangup() does not return until the port has been completely shut down, even in the presence of a racing hangup operation. This change enforces strict ordering guarantees for resource cleanup, preventing premature returns and ensuring that all references to the TTY structure are properly invalidated before memory is released. It is important to note that the serial core already handles similar concerns correctly by holding the port mutex during uart_hangup(), so this fix primarily addresses gaps in other parts of the TTY subsystem. Administrators should apply kernel updates containing these patches immediately to restore proper synchronization and eliminate the risk associated with concurrent hangup operations.
This vulnerability aligns with CWE-362, which describes Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). The lack of mutual exclusion when modifying shared TTY port state allows for unsafe access patterns that compromise data integrity. Furthermore, from a cyber defense perspective, this issue relates to ATT&CK technique T1059, Command and Scripting Interpreter, as race conditions in kernel subsystems can sometimes be leveraged during post-exploitation phases to maintain persistence or escalate privileges after initial system compromise. By ensuring proper serialization of hangup operations, the fix strengthens the kernel's resistance against such exploitation vectors. Maintaining up-to-date kernels is essential for preserving these synchronization guarantees and protecting against both accidental crashes and deliberate malicious exploitation attempts targeting TTY subsystem weaknesses.