CVE-2026-23191

In the Linux kernel, the following vulnerability has been resolved:

ALSA: aloop: Fix racy access at PCM trigger

The PCM trigger callback of aloop driver tries to check the PCM state and stop the stream of the tied substream in the corresponding cable. Since both check and stop operations are performed outside the cable lock, this may result in UAF when a program attempts to trigger frequently while opening/closing the tied stream, as spotted by fuzzers.

For addressing the UAF, this patch changes two things:

• It covers the most of code in loopback_check_format() with cable->lock spinlock, and add the proper NULL checks. This avoids already some racy accesses.
• In addition, now we try to check the state of the capture PCM stream that may be stopped in this function, which was the major pain point leading to UAF.

This vulnerability is rated as Moderate impact because exploitation requires local access and interaction with the ALSA loopback driver, which is neither loaded nor used by default in typical Red Hat Enterprise Linux environments. A local unprivileged attacker could trigger the race condition during concurrent audio stream state transitions, potentially leading to kernel memory corruption or a denial of service. Because the attack cannot be conducted remotely and depends on the presence of an optional virtual soundcard module, the overall blast radius is significantly constrained.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.