CVE-2026-23076: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-23076 Overview

CVE-2026-23076 is an out-of-bounds access vulnerability [CWE-125] in the Linux kernel's ALSA ctxfi audio driver. The flaw resides in the audio mixer handling code, specifically within the amixer_index() and sum_index() callbacks in sound/pci/ctxfi/ctamixer.c. The conf field functions as a loop index but lacks proper (re-)initialization, allowing the index to exceed the bounds of an 8-element unsigned char array. Fuzzers detected the issue through UBSAN reporting index 8 is out of range for type 'unsigned char [8]'. The vulnerability affects the Linux kernel 6.19 release candidates and earlier branches receiving stable backports.

Critical Impact
Local attackers with low privileges can trigger out-of-bounds memory access in the kernel, leading to information disclosure or denial of service through kernel crashes.

Affected Products

Linux Kernel 6.19-rc1 through 6.19-rc6
Linux Kernel stable branches receiving backported ctxfi driver code
Systems using Creative Sound Blaster X-Fi cards backed by the ctxfi ALSA driver

Discovery Timeline

2026-02-04 - CVE-2026-23076 published to NVD
2026-03-18 - Last updated in NVD database

Technical Details for CVE-2026-23076

Vulnerability Analysis

The vulnerability exists in the Advanced Linux Sound Architecture (ALSA) ctxfi driver, which supports Creative Technology X-Fi audio hardware. The driver maintains a conf field used as a loop index when iterating over mixer resources. This index is consumed by the amixer_index() and sum_index() callback functions to dereference into fixed-size arrays declared as unsigned char [8].

Fuzzing identified that the conf field is not consistently (re-)initialized across allocation and reuse paths. When stale or attacker-influenced values remain in the field, the callbacks dereference past the array boundary. UBSAN flagged the condition at sound/pci/ctxfi/ctamixer.c:347 with index 8 is out of range for type 'unsigned char [8]'.

Root Cause

The root cause is missing initialization of the conf loop index inside the mixer and summing resource management routines. Without explicit reset between allocations, the field retains uninitialized or previously written values. Because the index is later used as an array offset without bounds checking, the resulting read accesses memory adjacent to the intended buffer.

Attack Vector

Exploitation requires local access with low privileges to a system that exposes the ctxfi driver. An attacker interacting with the ALSA mixer interface, typically through /dev/snd/* device nodes or the ioctl interface, can drive the driver into states where the uninitialized conf index is referenced. The result is an out-of-bounds read [CWE-125] that can disclose adjacent kernel memory or destabilize the kernel and cause a denial of service. Successful exploitation does not require user interaction. See the upstream kernel patch for the corrective changes that add proper initialization of the loop indices.

Detection Methods for CVE-2026-23076

Indicators of Compromise

UBSAN kernel log entries referencing array-index-out-of-bounds in sound/pci/ctxfi/ctamixer.c
Kernel oops or panic traces originating from amixer_index() or sum_index()
Unexpected crashes of audio-dependent userland processes invoking ALSA mixer ioctls

Detection Strategies

Monitor dmesg and /var/log/kern.log for UBSAN reports mentioning the ctxfi driver or ctamixer.c
Audit installed kernel versions against the fixed commits listed in the kernel.org stable advisories
Identify hosts loading the snd_ctxfi module using lsmod and inventory exposure

Monitoring Recommendations

Enable CONFIG_UBSAN and CONFIG_UBSAN_BOUNDS on test kernels to surface similar out-of-bounds conditions
Forward kernel ring buffer events to a centralized logging pipeline for anomaly review
Track unprivileged process access to /dev/snd/* device nodes on multi-user systems

How to Mitigate CVE-2026-23076

Immediate Actions Required

Apply the upstream Linux kernel patches referenced in the kernel.org stable commits for affected branches
Update to a distribution kernel that incorporates the ALSA: ctxfi initialization fix
Restrict local access to multi-user systems with the ctxfi driver loaded until patches are deployed

Patch Information

The Linux kernel maintainers released fixes across multiple stable branches. The corrective patches initialize the conf loop index before it is referenced by amixer_index() and sum_index(). Relevant commits include 61006c540cbd, 6524205326e0, 873e2360d247, 8c1d09806e14, a8c42d11b052, afca7ff5d5d4, and d77ba72558cd. Administrators should apply the patch matching their kernel branch and reboot into the corrected build.

Workarounds

Unload the snd_ctxfi kernel module with modprobe -r snd_ctxfi on systems that do not require Creative X-Fi audio
Blacklist the module by adding blacklist snd_ctxfi to /etc/modprobe.d/blacklist-ctxfi.conf
Tighten permissions on /dev/snd/* to limit access to trusted users and groups

bash

# Configuration example
echo 'blacklist snd_ctxfi' | sudo tee /etc/modprobe.d/blacklist-ctxfi.conf
sudo modprobe -r snd_ctxfi
sudo update-initramfs -u