CVE-2025-71192: Linux Kernel Use-After-Free Vulnerability

CVE-2025-71192 Overview

CVE-2025-71192 is a Double Free vulnerability in the Linux kernel's ALSA (Advanced Linux Sound Architecture) AC97 subsystem. The vulnerability exists in the snd_ac97_controller_register() function where improper memory management can lead to a double free condition when ac97_add_adapter() fails.

The issue occurs because when ac97_add_adapter() fails, the code incorrectly uses kfree() when put_device() is the correct way to drop the device reference. This improper cleanup logic can result in memory being freed twice, potentially leading to memory corruption or system instability.

Critical Impact

Double free vulnerabilities in kernel subsystems can lead to memory corruption, kernel panic, denial of service, or potentially privilege escalation in certain exploitation scenarios.

Affected Products

• Linux Kernel (ALSA AC97 subsystem)
• Systems utilizing AC97 audio codec controllers
• Linux-based devices with AC97 sound hardware support

Discovery Timeline

• 2026-02-04 - CVE CVE-2025-71192 published to NVD
• 2026-02-04 - Last updated in NVD database

Technical Details for CVE-2025-71192

Vulnerability Analysis

The double free vulnerability resides in the snd_ac97_controller_register() function within the Linux kernel's ALSA AC97 audio driver subsystem. When the ac97_add_adapter() function fails during device registration, the error handling path incorrectly calls kfree() on memory that will also be freed by the device subsystem's reference counting mechanism.

In the Linux kernel device model, when a device structure is allocated and registered, the proper way to release it upon failure is through put_device(), which decrements the reference count and triggers the device's release function. The release function (ac97_adapter_release()) is responsible for freeing the device structure. By calling kfree() directly in addition to the implicit free from the device model, the same memory region gets freed twice.

Additionally, the fix addresses a missing kfree() call when idr_alloc() fails, ensuring proper cleanup in that error path as well.

Root Cause

The root cause is improper memory management in error handling paths within snd_ac97_controller_register(). The code failed to properly understand the device reference counting model, leading to redundant explicit kfree() calls where only put_device() should be used. The fix ensures that:

1. When ac97_add_adapter() fails, only put_device() is called (removing the erroneous kfree())
2. When idr_alloc() fails, proper kfree() is added since the device hasn't been registered yet
3. The ac97_adapter_release() function properly handles memory cleanup through the device model

Attack Vector

This vulnerability requires local access to a system running an affected Linux kernel version with AC97 audio hardware. An attacker would need to trigger the specific error condition in snd_ac97_controller_register() where ac97_add_adapter() fails. This could potentially be achieved through:

1. Manipulating device registration processes
2. Causing resource exhaustion that triggers adapter registration failures
3. Exploiting race conditions during audio subsystem initialization

While exploitation complexity is high due to the specific conditions required, successful exploitation of double free vulnerabilities can lead to kernel memory corruption, denial of service through kernel panic, or in sophisticated attacks, potential privilege escalation through heap manipulation techniques.

Detection Methods for CVE-2025-71192

Indicators of Compromise

• Unexpected kernel panics or oops messages referencing ALSA or AC97 subsystem
• Memory corruption warnings in kernel logs related to audio driver initialization
• System instability during audio device detection or driver loading
• SLUB/SLAB allocator warnings about double free or use-after-free conditions

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for ALSA AC97-related errors and memory corruption warnings
• Deploy kernel address sanitizer (KASAN) on test systems to detect memory safety violations
• Use SentinelOne's kernel-level monitoring to detect anomalous memory operations in audio subsystems
• Implement audit rules to track audio device registration failures and related system calls

Monitoring Recommendations

• Enable kernel memory debugging features (CONFIG_DEBUG_SLAB, CONFIG_SLUB_DEBUG) in development environments
• Monitor for repeated AC97 adapter registration failures which may indicate exploitation attempts
• Configure alerting for kernel oops or panic events with backtraces containing snd_ac97 function names
• Review system stability metrics for correlation with audio driver activity

How to Mitigate CVE-2025-71192

Immediate Actions Required

• Update to a patched Linux kernel version that includes the fix for this vulnerability
• Review systems with AC97 audio hardware for signs of instability or compromise
• Consider disabling AC97 audio support if not required and patching is not immediately possible
• Restrict local access to systems until patches can be applied

Patch Information

The vulnerability has been resolved in the Linux kernel with multiple commits across stable branches. The fix corrects the error handling in snd_ac97_controller_register() to properly use put_device() instead of kfree() when ac97_add_adapter() fails, and adds proper cleanup when idr_alloc() fails.

Patches are available through the following kernel commits:

• Kernel Commit 21f8bc5179be
• Kernel Commit 830988b6cf19
• Kernel Commit c80f9b3349a9
• Kernel Commit cb73d37ac18b
• Kernel Commit fcc04c92cbb5

Workarounds

• If immediate patching is not feasible, consider blacklisting the snd_ac97_codec module if AC97 audio is not required
• Limit local user access to reduce the attack surface for exploitation
• Monitor affected systems closely for signs of kernel instability or exploitation attempts
• Deploy SentinelOne endpoint protection for real-time kernel behavior monitoring

# Temporarily disable AC97 audio module if not needed
echo "blacklist snd_ac97_codec" >> /etc/modprobe.d/blacklist-ac97.conf
echo "blacklist snd_ac97_bus" >> /etc/modprobe.d/blacklist-ac97.conf

# Update initramfs to apply module blacklist
update-initramfs -u

# Check current kernel version and compare with patched versions
uname -r