CVE-2025-39757

What it actually does

The vulnerability allows out-of-bounds memory accesses when processing UAC3 class segment descriptors in USB audio devices due to insufficient validation of descriptor sizes against declared lengths and buffer allocations.

Why it matters to the business

Systems using USB audio devices risk memory corruption leading to crashes, data exposure, or privilege escalation; with 411 days since publication and references to threat actors like VMSCAPE, delayed patching increases exposure across Linux environments with high ecosystem prevalence.

How an attack unfolds

An attacker supplies a malicious USB device emitting malformed UAC3 descriptors; upon connection the ALSA usb-audio driver parses them without size checks against declared lengths or buffers, enabling OOB accesses. Threat actors such as VMSCAPE may chain this with related kernel issues for escalation.

How to fix it

Apply the kernel fix from commit 799c06ad4c9c790c265e8b6b94947213f1fb389c in org/pub/scm/linux/kernel/git/stable/linux.git or upgrade to a stable release containing this change.

How to confirm the fix worked

Confirm the fix commit is present in the running kernel source; test descriptor parsing with crafted UAC3 devices in a controlled environment to verify no OOB occurs.

Typical attack path

1. Connect malicious USB audio device to target system
2. Kernel detects device and loads usb-audio driver
3. Driver reads UAC3 cluster segment descriptors without validation
4. Size mismatch triggers out-of-bounds memory access

How to detect it

Review kernel logs for USB audio descriptor parsing failures or crashes; monitor for connections of unrecognized USB audio devices in system and audit logs, especially in contexts involving VMSCAPE or similar campaigns.

What your security team should do

• Immediately update kernels on all systems exposing USB audio functionality
• Restrict untrusted USB device connections until patched
• Incorporate commit 799c06ad4c9c790c265e8b6b94947213f1fb389c into internal build pipelines