CVE-2024-42121

What it actually does

The vulnerability permits an invalid msg_id value (including MOD_HDCP_MESSAGE_ID_INVALID or negative) to be used directly as an array index without validation, resulting in out-of-bounds read or write operations in the AMD display HDCP message handling code.

Why it matters to the business

Kernel instability, potential crashes, or memory corruption on AMD GPU systems can lead to denial of service, degraded graphics performance, or in rare cases local privilege escalation, increasing operational risk for Linux-based servers, workstations, and embedded devices.

How an attack unfolds

An attacker with local access supplies or triggers an HDCP message path where msg_id evaluates to an invalid index; the unchecked value is then used for array access, causing memory corruption that may be leveraged for further exploitation.

How to fix it

Apply the upstream fix by updating to a kernel containing commit b5b8837d066cc182ff69fb5629ad32ade5484567 or later; rebuild and deploy the patched kernel across all affected AMD-based Linux systems.

How to confirm the fix worked

Confirm the presence of commit b5b8837d066cc182ff69fb5629ad32ade5484567 in the running kernel source tree or verify that the msg_id validation check exists before any array access in drm/amd/display HDCP code paths.

Typical attack path

1. Obtain local execution context on an affected Linux system with AMD display hardware
2. Trigger or manipulate HDCP message handling to set msg_id to -1 or MOD_HDCP_MESSAGE_ID_INVALID
3. Cause the kernel to perform an array read or write using the unchecked index
4. Exploit resulting memory corruption to achieve crash, information leak, or code execution

How to detect it

Review kernel logs for unexpected crashes or oops messages originating from drm/amd/display HDCP message handling; examine any user-space processes that interact with display or HDCP interfaces for anomalous behavior around message ID values.

What your security team should do

• Prioritize kernel upgrade to the fixed commit on all AMD GPU Linux hosts within the next patching cycle
• Monitor for any downstream distribution backports of b5b8837d066cc182ff69fb5629ad32ade5484567
• Review systems using AMD display drivers for exposure and schedule maintenance windows accordingly
• Harden local access controls to reduce the attack surface while patches are applied