CVE-2024-56696

What it actually does

Unchecked return values from kunit_kzalloc() in sound_kunit.c allow NULL pointer dereference in the ALSA core of the Linux kernel, resulting in memory corruption.

Why it matters to the business

Kernel instability or crashes during sound subsystem testing can disrupt development, validation workflows, and production systems using affected kernel builds, increasing downtime risk especially in environments with high downstream kernel dependents.

How an attack unfolds

An attacker with local access crafts conditions where kunit_kzalloc() returns NULL in sound_kunit.c paths; dereferencing the pointer without a check triggers the NULL dereference. Listed threat actors involved in 2024 zero-day campaigns and Linux kernel memory issues could leverage similar patterns for denial of service or further corruption.

How to fix it

Update to fixed kernel commit f5486bf8abfe778b368d8fd1aa655dc01d0013ca or apply equivalent patches adding NULL checks after every kunit_kzalloc() call in sound_kunit.c. For listed libarchive packages on Ubuntu 14.04 LTS upgrade to 3.1.2-7ubuntu2.4 and on 16.04 LTS to 3.1.2-11ubuntu0.16.04.3.

How to confirm the fix worked

Confirm kernel source contains NULL checks after all kunit_kzalloc() invocations in sound_kunit.c; rebuild and run kunit tests to verify no dereference occurs on allocation failure; check package versions against the listed fixed releases.

Typical attack path

1. Identify systems running vulnerable kernel versions with ALSA kunit test code enabled
2. Trigger kunit test execution or equivalent allocation paths that invoke kunit_kzalloc()
3. Force allocation failure to return NULL
4. Execute code path that dereferences the unchecked pointer
5. Cause kernel panic or memory corruption for denial of service or escalation

How to detect it

Review kernel logs for NULL pointer dereference oops in ALSA or kunit paths; correlate with execution of sound-related test suites. Threat actor mentions of Linux kernel memory issues provide context for hunting similar patterns but no specific post-exploitation artifacts are known.

What your security team should do

• Prioritize patching kernel builds to the fixed commit within standard change windows given stable low EPSS
• Audit any custom ALSA kunit test usage for similar unchecked allocations
• Monitor for kernel oops or panic logs referencing sound_kunit.c
• Track EPSS trend and any new threat actor activity around Linux kernel memory flaws