CVE-2026-23089 in Linux
Summary
by MITRE • 02/04/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: usb-audio: Fix use-after-free in snd_usb_mixer_free()
When snd_usb_create_mixer() fails, snd_usb_mixer_free() frees mixer->id_elems but the controls already added to the card still reference the freed memory. Later when snd_card_register() runs, the OSS mixer layer calls their callbacks and hits a use-after-free read.
Call trace: get_ctl_value+0x63f/0x820 sound/usb/mixer.c:411 get_min_max_with_quirks.isra.0+0x240/0x1f40 sound/usb/mixer.c:1241 mixer_ctl_feature_info+0x26b/0x490 sound/usb/mixer.c:1381 snd_mixer_oss_build_test+0x174/0x3a0 sound/core/oss/mixer_oss.c:887 ... snd_card_register+0x4ed/0x6d0 sound/core/init.c:923 usb_audio_probe+0x5ef/0x2a90 sound/usb/card.c:1025
Fix by calling snd_ctl_remove() for all mixer controls before freeing id_elems. We save the next pointer first because snd_ctl_remove() frees the current element.
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Analysis
by VulDB Data Team • 05/03/2026
The vulnerability identified as CVE-2026-23089 represents a critical use-after-free condition within the Linux kernel's ALSA USB audio subsystem, specifically affecting the snd_usb_mixer_free() function. This flaw occurs during the USB audio device initialization process when the snd_usb_create_mixer() function encounters a failure condition. The vulnerability stems from improper memory management where the mixer->id_elems structure gets freed while still referenced by control elements that have already been registered with the audio card. The technical implementation reveals that when the mixer creation fails, the system attempts to clean up by freeing the id_elems memory structure, but the individual control elements that were previously added to the card retain pointers to this now-freed memory location. This memory management inconsistency creates a scenario where subsequent operations on the audio card can trigger memory access violations.
The operational impact of this vulnerability extends beyond simple system instability, potentially enabling arbitrary code execution or denial of service conditions within the audio subsystem. The call trace demonstrates how the vulnerability manifests when snd_card_register() executes and the OSS mixer layer attempts to invoke callbacks on the freed control elements. The specific sequence shows that get_ctl_value() function accesses memory that has already been freed, leading to a use-after-free read condition that can result in unpredictable behavior. This vulnerability affects the core audio subsystem functionality and can be exploited by malicious actors to compromise system integrity, particularly in environments where USB audio devices are frequently connected and disconnected. The vulnerability aligns with CWE-416, which describes the use of freed memory condition, and represents a classic memory safety issue in kernel space programming.
The fix implemented addresses the root cause by ensuring proper cleanup of control elements before freeing the id_elems structure. The solution involves calling snd_ctl_remove() for all mixer controls before the id_elems memory is freed, with the critical implementation detail of preserving the next pointer before removal since snd_ctl_remove() itself frees the current element. This approach prevents the dangling pointer references that lead to the use-after-free condition. The mitigation strategy follows established security best practices for kernel memory management and aligns with ATT&CK techniques related to privilege escalation and system resource manipulation. The fix ensures that all control elements are properly deregistered from the audio card before their memory is released, preventing any subsequent access to freed memory locations. This remediation approach maintains the integrity of the ALSA subsystem while preserving the expected functionality of USB audio device management, addressing both immediate security concerns and long-term system stability requirements.