CVE-2026-98742 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: seq: Serialize compat port-info ioctls
The native sequencer ioctl path serializes handler calls with client->ioctl_mutex, but the translated port-info compat path invokes the same handlers through snd_seq_kernel_client_ctl() without taking that mutex.
This lets concurrent compat CREATE_PORT requests pass the port-count check before any request reaches the serialized insertion. The computed integer port index can then exceed the address field range and wrap to an existing index. Subsequent subscriber teardown can resolve the duplicate address to the wrong port and access a freed subscriber.
Take ioctl_mutex while dispatching converted port-info requests, matching the native ioctl path. All translated port-info commands share this helper, so their accesses to the client port state are serialized as well.
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Analysis
by VulDB Data Team • 10/19/2026
The Linux kernel's Advanced Linux Sound Architecture (ALSA) sequencer subsystem contains a concurrency vulnerability arising from inconsistent locking mechanisms in its compatibility layer for 32-bit applications running on 64-bit systems. The native ioctl path correctly serializes handler calls by acquiring the client-specific ioctl_mutex, ensuring that operations such as creating ports are atomic with respect to other port management actions. However, the translated port-info compat path invokes these same handlers through the snd_seq_kernel_client_ctl function without acquiring this mutex. This discrepancy creates a race condition where concurrent CREATE_PORT requests from compatibility mode can bypass critical checks designed to prevent resource exhaustion or state corruption. Specifically, multiple threads may pass the port-count validation check simultaneously before any single request is processed by the serialized insertion logic that enforces mutual exclusion.
This lack of serialization allows an attacker to exploit the timing window between the initial count verification and the actual port creation. The computed integer port index can exceed the valid address field range due to concurrent modifications, causing it to wrap around or collide with an existing index. When this occurs, subsequent subscriber teardown operations may incorrectly resolve a duplicate address to a different port than intended. This misdirection leads to use-after-free conditions where the system attempts to access memory associated with a subscriber that has already been freed by another thread. Such memory corruption can result in kernel panics, denial of service, or potentially arbitrary code execution if an attacker can carefully control the state of the freed memory and trigger specific dereferences during the race window.
From a vulnerability classification perspective, this issue aligns with CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization, as the core flaw is the failure to properly synchronize access to shared client port state data structures. In terms of attack vectors, it relates to ATT&CK techniques involving resource manipulation and potential privilege escalation through kernel memory corruption. The vulnerability highlights a common pitfall in Linux kernel development where compatibility layers for legacy 32-bit binaries must strictly mirror the synchronization primitives used by their native 64-bit counterparts to maintain security boundaries across architecture transitions.
The resolution involves modifying the compat ioctl handling code to acquire the ioctl_mutex while dispatching converted port-info requests, thereby matching the behavior of the native ioctl path. By ensuring that all translated port-info commands share this helper function and are serialized under the same mutex, concurrent access to client port state is prevented. This change eliminates the race condition by guaranteeing that only one thread can modify or inspect the port table at any given time during these operations. System administrators should apply kernel updates provided by their distribution vendors as soon as they become available to mitigate this risk. For environments where immediate patching is not possible, monitoring for unusual ALSA sequencer activity and restricting access to sound device nodes may provide limited mitigation against local exploitation attempts.