Linux Kernel CVE-2024-53050: i915 HDCP Fix Shields Against NULL Pointer Oops

A null-pointer defensive check added to the Intel i915 HDCP code (hdcp2_get_capability) closes a local denial‑of‑service vector tracked as CVE‑2024‑53050 by ensuring the encoder pointer is validated before use, turning an uncontrolled kernel oops into a deterministic error path and removing a reliable crash primitive from affected Linux kernels.

Background / Overview​

The vulnerability appears in the Linux kernel's Intel graphics DRM stack (drivers/gpu/drm/i915), specifically in the HDCP (High-bandwidth Digital Content Protection) handling for HDCP 2.x capability queries. The upstream change adds a simple but crucial encoder check inside the intel_hdcp2_get_capability (also referenced in some trees as hdcp2_get_capability) function to avoid dereferencing a NULL encoder pointer. This prevents kernel-space NULL-pointer dereferences that would otherwise produce a kernel oops or driver crash when certain code paths are exercised. Multiple vulnerability tracking sources (NVD, OSV, major distribution trackers) classify the issue as a medium-severity availability vulnerability with a CVSS v3.1 base score around 5.5 because the impact is denial-of-service (DoS) rather than confidentiality or integrity compromise. The public disclosure and advisories date to November 19, 2024, with distribution advisories and package updates following as maintainers backported the minimal fix into stable branches.

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Technical anatomy: what went wrong​

The driver context​

The Intel DRM i915 driver implements HDCP support for protected display links. Part of that support involves enumerating capabilities of connected receivers and encoders for HDCP2.x operations. When code that queries HDCP2 capabilities executes, it relies on a valid encoder object to be present and referenced.

Root cause​

A code path allowed the HDCP capability function to run without confirming that the encoder pointer was non‑NULL. In kernel space, dereferencing NULL is fatal—unlike userland where a process aborts, a kernel NULL dereference typically produces an oops, may crash the driver, and can lead to host instability or a panic. The fix inserted a defensive check that validates the encoder pointer before use, converting what could be an uncontrolled kernel fault into a safe error return. This is a classic defensive-programming correction that eliminates a local DoS primitive.

Scope in the source tree​

The vulnerable code lives under the i915 DRM path (drivers/gpu/drm/i915/hdcp*), and the change is intentionally small—an added conditional to guard the encoder dereference. Kernel maintainers favored a surgical commit that is easy to backport into stable branches with minimal regression risk. OSV and stable-tree commit indexes show the fixed commits were merged into multiple stable releases.

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Affected systems and distribution status​

• Affected component: Linux kernel — Intel DRM i915 HDCP code.
• Typical exposure: systems running kernels that contain the vulnerable commit range prior to the backported fix. Distribution trackers list specific fixed package versions for their release trees; upstream repositories identify fixed commits and the revision at which the issue was corrected.

Distribution and vendor mapping at time of publication:

• Ubuntu published an advisory and classed the issue as Medium (CVSS 5.5). Administrators should confirm package-level statuses and upgrade to patched kernel images where available.
• Debian tracking shows package statuses per release, with newer unstable/testing packages carrying the fix while older stable branches may still be listed as vulnerable until backports are applied. Operators should consult their distribution’s tracker for fixed package versions.
• OSV and other vulnerability mirrors list the fixed commit(s) and the git events that introduced and remediated the issue; maintainers used these artifacts to create distribution packages and advisories.

Practical note: kernel package names, maintenance policies, and backport schedules vary. Embedded device vendors and OEM kernels commonly lag upstream and therefore represent the most likely long‑tail exposure. Cloud images and appliance kernels should be inventoried individually to confirm whether they include the fixed commit.

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Exploitability and real‑world impact​

Attack vector and prerequisites​

• Attack vector: Local. The HDCP capability path is exercised by local code interacting with the DRM stack (for example, compositors, user-mode utilities, or local device management tools). An unprivileged local process may be able to trigger the path in some configurations where DRM device nodes are accessible.
• Privileges required: Low (often unprivileged in desktop/embedded contexts), but the practical ability to trigger the exact path depends on system configuration and what device nodes are exposed to userland.
• Complexity: Low. The condition is deterministic and requires only exercising the particular HDCP capability query path with a missing/NULL encoder state.

Practical impact​

• Primary impact: Availability — kernel oops, driver crash, or host instability. Recovery typically requires a driver reload or reboot.
• Confidentiality and integrity: None reported. There is no evidence this issue enables privilege escalation or arbitrary code execution on its own.
• Real‑world evidence: As of disclosure and subsequent advisories, there were no widely reported in‑the‑wild exploits weaponizing this specific CVE; its attractiveness is mainly as a DoS primitive in multi‑user or multi‑tenant environments.

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How the fix works​

The patch is deliberately small: before the function uses the encoder pointer it now checks whether the encoder object is present (non‑NULL). If the encoder is missing the function returns an appropriate error rather than dereferencing NULL. Because the change is localized and behavior-preserving for correctly-configured hardware, it is straightforward to backport into stable kernel branches and to land in distribution kernels with low regression risk. OSV and kernel stable-tree entries link to the commits used for remediation. This pattern—adding small defensive checks at hardware abstraction boundaries—is a common and effective way to remove crash primitives from kernel drivers without changing the intended behavior for correct hardware configurations. Similar defensive corrections across DRM drivers have been used repeatedly to convert oops‑prone flows into recoverable probe errors.

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Detection and forensic signals​

When hunting for this class of bug or verifying whether it has been triggered, focus on operational evidence rather than stealthy indicators:

• Kernel oops/panic stack traces naming functions such as intel_hdcp2_get_capability or related i915 HDCP frames, or log lines indicating a NULL pointer dereference in i915/hdcp code paths.
• Repeated driver crashes correlated with display reconfiguration events or with HDCP-capability probes after monitor hot-plug events.
• dmesg and journalctl -k entries that include kernel oops traces referencing i915 or DRM functions.
• For embedded devices or appliances, collect serial console logs during boot and during repro attempts; these often capture kernel oops traces not written to persistent system logs. Operational detection can rely on SIEM rules that match known function names and oops text signatures.

Post‑fix verification: inspect kernel package changelogs for your distribution release, confirm the kernel version or package includes the stable commit ID(s) associated with CVE‑2024‑53050, then reboot into the patched kernel and validate display operations across your hardware topologies.

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Remediation checklist (actionable)​

• Inventory: Enumerate systems that run the Intel i915 driver and where GPU/DRM device nodes are present:
• uname -r to show running kernel version.
• lsmod | grep i915 to check if the module is loaded.
• ls -l /dev/dri/* to see device node permissions and groups.
• Verify fix availability:
• Consult your distribution’s security tracker or package changelog for CVE‑2024‑53050 and the fixed kernel package versions.
• OSV/NVD/Ubuntu/Debian advisories will list affected and fixed ranges; cross-reference them for your platform.
• Patch:
• Install the vendor- or distro-supplied kernel update that includes the backported stable commit, then reboot to activate the fix.
• For custom kernels, cherry‑pick the stable commit(s) that fix CVE‑2024‑53050 into your tree and rebuild. Test on representative hardware before wide deployment.
• Compensating controls if immediate patching is impossible:
• Restrict access to DRM device nodes: create udev rules to bind /dev/dri/* to a trusted group and remove access for untrusted users or containers.
• Avoid exposing DRM devices to untrusted containers or CI runners (remove --device=/dev/dri and related passthrough).
• Monitor kernel logs for i915 oops signatures and alert on repeated crashes.
• Validate:
• After patch and reboot, run representative display workloads, exercise HDCP-capable paths (if safe and permitted), and monitor stability for at least 24–72 hours.
• Ensure vendor-provided firmware for docking stations or external adapters is also up to date when such gear interacts with the display stack.

These steps follow standard kernel remediation best practice and echo prior operational guidance used for similar DRM-related fixes across the kernel.

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Critical analysis: strengths of the fix and residual risks​

Strengths​

• Surgical fix: The change is minimal and behavior-preserving for correctly-configured hardware, making it low-risk to backport and deploy in stable kernels.
• Availability-focused remediation: By converting a NULL dereference into a controlled error path, the patch eliminates a deterministic DoS primitive without changing the intended HDCP functionality.
• Verifiable artifacts: Stable-tree commit IDs and distribution advisories provide clear points of verification for administrators to confirm remediation. OSV/NVD/Ubuntu/Debian tracking entries document the fix and the affected package ranges.

Residual risks and practical caveats​

• Vendor and embedded lag: The principal remaining risk is the long tail of vendor-supplied kernels in embedded devices, appliances, and OEM images. These may not receive timely backports and therefore remain vulnerable. Operators must inventory and coordinate with vendors for firmware/kernel updates.
• Exposure by configuration: Systems that deliberately expose DRM devices to untrusted users or containers (multi‑tenant GPU hosts, CI runners) remain at elevated risk until patched or mitigated by access controls.
• Detection blind spots: Kernel oops traces can be lost without proper log retention, crash dumps, or serial logging. Devices that do not persist kernel ring buffers may not show a clear trail of exploitation attempts.
• Over-reliance on numeric scores: CVSS numbers differ across trackers; prioritize remediation by exposure and business impact rather than a single numeric severity. Several previous DRM fixes show similar scoring variance even though operational exposure is the true triage determinant.

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Operational recommendations for administrators and integrators​

• Treat this CVE as a standard kernel update priority: identify exposed systems, schedule a staged kernel update (pilot → staging → production), and validate on representative hardware.
• For multi‑tenant environments, enforce strict device access policies: limit /dev/dri to trusted groups and do not bind-pass devices to untrusted containers.
• For embedded fleets and appliances, establish a vendor management process to request and track backport timelines or to coordinate a rebuild that includes upstream stable commits.
• Enhance kernel logging and retention so that any future kernel oops in DRM subsystems yield forensic traces to accelerate triage.
• Maintain a staging pool of hardware configurations that represent your field diversity (laptops, desktops, docking setups) to validate fixes across realistic scenarios.

These recommendations align with lessons from prior DRM and SoC driver fixes where small defensive commits prevented high-impact availability issues while requiring careful operational rollout to avoid regressions.

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Broader lessons for driver authors and security teams​

• Defensive checks at hardware and probe boundaries matter: adding explicit validations for pointers and state transitions is a low-cost way to remove crash primitives.
• Keep selftests and driver test harnesses robust: even test-oriented code or mock paths can be exercised in the field or by integration tests; they should not assume invariants without explicit checks.
• Prioritize easy-to-backport surgical fixes: small patches are more likely to be adopted across stable branches and vendor kernels, narrowing the long‑tail exposure window.
• Inventory vendor‑supplied kernels as part of standard vulnerability management: many embedded and OEM images include downstream kernels that diverge from distribution trees, and those images often lag upstream fixes.

Similar remediation approaches and the operational playbook used here have repeatedly reduced kernel DoS exposure across various DRM subsystems; the community’s practice of favoring minimal, well-tested backports reduces regression risk and helps operators remediate broadly.

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Conclusion​

CVE‑2024‑53050 is a localized, availability‑oriented Linux kernel vulnerability in the Intel i915 HDCP capability path that was remedied with a minimal but important encoder pointer validation. The fix reduces the risk of kernel oops and host instability by converting an unsafe NULL dereference into a controlled error return. Operators should treat the issue as a medium‑priority kernel update for systems that expose DRM device nodes to local users or run vendor kernels that may lag upstream. Verify fixes via distribution advisories and stable-tree commit IDs, apply kernel updates in a staged manner, and — where patching is delayed — apply compensating controls such as restricting /dev/dri access and improving kernel log retention and monitoring.

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Source: MSRC Security Update Guide - Microsoft Security Response Center