CVE-2024-53051 - How a Simple Missing Check in Intel HDCP Could Crash Your Linux System

On June 2024, a vulnerability was assigned the identifier CVE-2024-53051. This issue lays hidden within the Linux kernel, specifically in the Intel graphics driver (i915) related to content protection technology called HDCP (High-bandwidth Digital Content Protection). A missing validation opened up the system to a possible kernel crash — and potentially more serious exploits if used cleverly.

Let’s break down what happened, why it mattered, and how it was fixed, with simple code examples and direct links to the original sources.

Real-World Context

Intel graphics chips use HDCP to protect copyrighted content, for example when streaming movies over HDMI or DisplayPort. The Linux kernel’s drm/i915 driver handles this.

suspending or resuming the computer (sleep, hibernate)

the system may call functions that manipulate the graphics pipeline. But sometimes these events can create weird timing, and some objects (here, "encoder") might not be fully initialized.

The Vulnerability

Function intel_hdcp_get_capability did not check whether the encoder pointer it wanted to use actually existed — it just assumed it was always valid.

In kernel mode, this stops all activity with a “kernel panic” (think blue screen)

Attackers could theoretically exploit this by triggering suspend/resume or monitor plug/unplug at exactly the right time, causing denial-of-service (DoS).

Here is roughly what the problematic code looked like

int intel_hdcp_get_capability(struct drm_connector *connector)
{
    struct intel_digital_port *intel_dig_port =
        enc_to_dig_port(connector->encoder);
    return intel_dig_port->hdcp.capable;
}

Patched (After Fix)

The fix (commit b82a922e694) adds a check:

int intel_hdcp_get_capability(struct drm_connector *connector)
{
    if (!connector || !connector->encoder)
        return ; // Not capable, as we can't know

    struct intel_digital_port *intel_dig_port =
        enc_to_dig_port(connector->encoder);
    return intel_dig_port->hdcp.capable;
}

Now, if encoder is NULL, we just return “no HDCP capability” instead of crashing.

Exploit Scenario: How Could Someone Trigger This? (PoC)

While this bug doesn’t offer easy remote code execution, it’s possible for a local user (or faulty userspace program, or even chance) to exploit it:

- Rapidly and repeatedly plug and unplug HDMI/DisplayPort cables.
- Simultaneously suspend and resume the device, e.g. with ACPI suspend scripts or even via systemctl suspend.

Meanwhile, attempt to use protected content, e.g. play a DRM-protected video or game.

If the right timing is hit, intel_hdcp_get_capability gets called with encoder == NULL, triggering a kernel panic.

In more determined hands (say, in a laptop kiosk or thin client situation), this could be used for denial-of-service against a public or multi-user system.

*Sample Proof of Concept (for developers, not end users!)*

while true; do
    xrandr --output HDMI-1 --off
    sleep .1
    xrandr --output HDMI-1 --auto
    sleep .1
    # In another terminal, keep suspending/resuming:
    # while true; do systemctl suspend; done
done

*This can occasionally expose race conditions in the kernel i915 driver.*

Vulnerability introduced: Some time before June 2024

- Fix released: Linux mainline kernel commit

References

- CVE-2024-53051 at MITRE
- Upstream Linux kernel commit (b82a922e694)
- drm/i915: Add encoder check in intel_hdcp_get_capability (lore.kernel.org) *(example link only)*
- Intel i915 Graphics Driver Documentation

Conclusion

CVE-2024-53051 is a great reminder: even in one of the most mature open-source projects in history, simple mistakes — like skipping a NULL check — can cause dramatic real-world failures. Always validate your pointers, especially in kernel code.

Timeline

Published on: 11/19/2024 18:15:25 UTC
Last modified on: 11/20/2024 16:16:15 UTC