CVE-2026-98754 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
tty: vcc: hold port lock when clearing tty pointer in vcc_cleanup
vcc_cleanup() sets port->tty to NULL without holding port->lock, racing with vcc_event() LDC callbacks that read port->tty under port->lock and then use tty->port. This can cause a use-after-free when the callback dereferences tty->port after cleanup has already destroyed and freed it.
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Analysis
by VulDB Data Team • 10/19/2026
The Linux kernel's virtual channel communication subsystem contains a concurrency flaw within the vcc_cleanup function that leads to a critical race condition involving terminal port management structures. The vulnerability arises because vcc_cleanup sets the port pointer of the tty structure to NULL without acquiring the associated port lock. This lack of synchronization creates a window where concurrent operations can access freed memory, specifically when other kernel threads or interrupt handlers interact with the same tty object simultaneously.
The core technical flaw is a classic use-after-free scenario driven by improper locking discipline. While vcc_cleanup proceeds to nullify and eventually free the underlying port structure, it does not hold the necessary spinlock that protects this data from concurrent modification. Simultaneously, the vcc_event function processes LDC callbacks which do acquire the port lock before reading the tty pointer. However, because the cleanup operation bypasses this locking mechanism entirely, there is no mutual exclusion between the deallocation of resources and their subsequent access by event handlers. This discrepancy allows a callback to read a valid-looking tty pointer that has already been logically removed from active use but not yet fully reclaimed by the memory allocator, or worse, dereference it after the underlying port structure has been freed entirely.
From an operational perspective, this race condition can result in kernel panics, system instability, or potential privilege escalation if an attacker can trigger the specific timing window where cleanup and event processing overlap. The impact is particularly severe because it affects fundamental I/O subsystems that are frequently accessed during normal system operation as well as under load conditions. Exploitation would likely require precise timing to force the race condition, but given its location in core kernel infrastructure, even rare occurrences can lead to significant denial of service or data corruption within the virtual channel communication layer.
This vulnerability is categorized under CWE-416 which describes use after free errors resulting from improper memory management and synchronization. In terms of attack vectors, it aligns with ATT&CK techniques related to exploitation for privilege escalation or system compromise through kernel-level vulnerabilities that bypass standard access controls due to logic flaws rather than simple input validation failures. The absence of proper locking mechanisms represents a fundamental deviation from secure coding practices required in concurrent environments where shared resources must be protected by atomic operations and mutexes.
To mitigate this risk, the primary remediation involves ensuring that all accesses to the tty port pointer are synchronized using the appropriate port lock. Developers must modify vcc_cleanup to acquire the port lock before setting the tty pointer to NULL, thereby preventing any concurrent callbacks from accessing or dereferencing the structure during its destruction phase. This ensures mutual exclusion between cleanup operations and event-driven reads, eliminating the race window entirely. Additionally, rigorous code review processes should enforce strict adherence to locking protocols for all shared kernel data structures to prevent similar concurrency bugs in other subsystems.