CVE-2026-98753 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
tty: tty_port: restore TTY_IO_ERROR on activation failure
Make sure to restore the TTY_IO_ERROR flag if activation fails to prevent I/O attempts on a port that is gone or powered down.
This specifically avoids issues like kernel panic due to unclocked accesses or NULL-pointer dereferences when accessing powered down or deregistered ports when a TTY ioctl races with hangup and open.
Note that the flag is set again in tty_port_close() but not restoring it on activation failure leaves a window where drivers fail to handle the ioctl-hangup race.
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Analysis
by VulDB Data Team • 10/19/2026
The Linux kernel's terminal subsystem, specifically within the tty port management layer, contains a logic flaw related to state synchronization during device activation and deactivation cycles. This vulnerability arises from an incomplete handling of error states when a TTY port fails to activate successfully. Under normal operation, the kernel manages various flags to track the status of serial or pseudo-terminal devices, ensuring that I/O operations are only directed toward active, powered-on, and registered hardware interfaces. However, in scenarios where the activation process encounters a failure condition, such as a race between an ioctl command requesting device access and a concurrent hangup event that deregisters or powers down the port, the system fails to properly restore critical error flags. Specifically, the TTY_IO_ERROR flag is not set when activation fails, leaving the internal state of the tty_port inconsistent with its actual physical availability.
This inconsistency creates a dangerous window where subsequent I/O attempts can be directed toward ports that are no longer accessible or powered down. Because the kernel believes the port is still in an active or neutral state rather than an error state, it proceeds to execute operations on hardware that may not respond correctly. This mismatch between software state and hardware reality leads to severe stability issues within the operating system. The most critical consequence of this flaw is a potential kernel panic caused by unclocked memory accesses or NULL-pointer dereferences. These crashes occur because drivers attempt to interact with registers or data structures associated with devices that have been removed from the bus or shut down, leading to undefined behavior and immediate system instability for any user space process interacting with these terminals.
From a security perspective, this vulnerability represents an availability risk due to its potential to cause denial of service through kernel crashes. It also touches upon integrity concerns if the race condition allows for unexpected state transitions that could be exploited in conjunction with other vulnerabilities. The flaw aligns with CWE-362, which describes concurrent execution errors and race conditions, as well as CWE-458 regarding incorrect initialization or incomplete configuration of system states. In terms of MITRE ATT&CK mapping, this type of issue falls under techniques related to exploitation for denial of service, particularly where kernel-level stability is compromised through improper state management during resource lifecycle events. The root cause lies in the failure to maintain strict atomicity and consistency checks when transitioning between open, closed, hung-up, and error states within the tty_port structure.
To mitigate this vulnerability, it is essential that system administrators ensure their Linux kernels are updated with patches that address this specific logic error in the tty subsystem. The fix involves modifying the activation failure path to explicitly restore the TTY_IO_ERROR flag, thereby preventing further I/O attempts on invalid ports until proper re-initialization occurs. This ensures that drivers correctly handle ioctl-hangup races by recognizing the port as unavailable rather than attempting access. For developers and maintainers of out-of-tree kernel modules or custom tty drivers, it is crucial to review any code that interacts with tty_port activation routines to ensure they respect these error flags. Regular security audits focusing on race conditions in device driver layers can help identify similar patterns where state synchronization failures might lead to stability issues or potential exploitation vectors involving memory corruption via null pointer dereferences.