CVE-2026-89943: Linux Kernel Use-After-Free Vulnerability

CVE-2026-89943 Overview

CVE-2026-89943 is a Linux kernel vulnerability in the ASoC (ALSA System on Chip) Loongson sound card driver. The flaw resides in the loongson_card_parse_acpi() function, which ignored the return value of device_property_read_string() when reading the codec-dai-name ACPI property. When the property is missing or invalid, the driver uses an uninitialized pointer, producing undefined behavior in kernel space.

Critical Impact
A local attacker with the ability to influence ACPI properties or trigger the driver's initialization path can cause kernel memory corruption, information disclosure, or denial of service through the uninitialized pointer dereference.

Affected Products

Linux kernel builds including the ASoC Loongson sound driver (sound/soc/loongson)
Loongson-based platforms using ACPI firmware to describe audio codec bindings
Distributions shipping kernels prior to the fixes referenced in the stable tree commits

Discovery Timeline

2026-09-16 - CVE-2026-89943 published to the National Vulnerability Database
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-89943

Vulnerability Analysis

The vulnerability is an Uninitialized Memory Use flaw in the ASoC Loongson driver's ACPI parsing path. In loongson_card_parse_acpi(), the driver calls device_property_read_string() to retrieve the codec-dai-name property but discards the function's return value. When the property is absent or malformed, the destination string pointer is never populated. The driver then continues execution and dereferences that uninitialized pointer.

Subsequent code paths use the value as a codec DAI name during sound card registration. This leads to undefined behavior ranging from arbitrary memory reads to kernel crashes. On systems where an attacker can influence firmware tables or provide a crafted ACPI description, the flaw can be triggered deterministically during driver probe.

Root Cause

The root cause is missing error handling around a property-read helper. Kernel API contract requires callers of device_property_read_string() to inspect the returned integer and abort initialization when the call fails. The Loongson card driver omitted this check, allowing execution to proceed with a stack or structure member that was never initialized.

Attack Vector

Exploitation requires local access with the ability to trigger the driver's probe path or influence ACPI firmware tables consumed by the kernel at boot. Impacts include high confidentiality, integrity, and availability loss, consistent with kernel-mode memory corruption. No network vector is present, and no user interaction is required beyond causing the driver to load.

No verified proof-of-concept code is publicly available. Details on the exact affected structures can be found in the upstream fix commits: Kernel Git Commit 0eb0e3c623 and Kernel Git Commit 4e580d84a6.

Detection Methods for CVE-2026-89943

Indicators of Compromise

Unexpected kernel oops or panic messages referencing loongson_card_parse_acpi or snd_soc during boot or module load
dmesg entries showing invalid pointer dereferences originating from the ASoC probe path on Loongson hardware
Repeated failures to bring up the audio subsystem accompanied by kernel stack traces

Detection Strategies

Inventory Linux hosts and identify kernels containing the vulnerable sound/soc/loongson driver without the patch commits applied
Compare running kernel versions against distribution advisories referencing the stable commits 0eb0e3c623, 4e580d84a6, 682c123cef, and bb1602908c6
Monitor endpoint telemetry for abnormal kernel crash frequencies on Loongson platforms

Monitoring Recommendations

Forward /var/log/kern.log and journald kernel messages to a centralized log platform for correlation
Alert on kernel taints, oops events, and module load failures involving ASoC components
Track ACPI table modifications and firmware changes on affected hardware fleets

How to Mitigate CVE-2026-89943

Immediate Actions Required

Apply the upstream Linux kernel patches referenced by commits 0eb0e3c623, 4e580d84a6, 682c123cef, and bb1602908c6
Update to a stable kernel release from your Linux distribution that includes the fix
Restrict local access to Loongson-based systems where patching cannot be completed immediately

Patch Information

The fix adds proper error handling: the return value of device_property_read_string() for codec-dai-name is now checked, and the error is propagated when the property is missing or invalid. Review the patches at Kernel Git Commit 682c123cef and Kernel Git Commit bb1602908c6 before backporting.

Workarounds

Blacklist the snd_soc_loongson_card module on systems that do not require audio functionality
Ensure ACPI firmware tables include a valid codec-dai-name property to avoid triggering the uninitialized path
Limit shell and physical access to reduce the chance of local exploitation while patches are staged

bash

# Blacklist the vulnerable module until patched
echo "blacklist snd_soc_loongson_card" | sudo tee /etc/modprobe.d/cve-2026-89943.conf
sudo update-initramfs -u
sudo reboot