CVE-2026-46314: Linux Kernel DRM v3d Infinite Loop DoS Vulnerability

Technical summary

The vulnerability exists in v3d_get_extensions(), which processes a user-controlled linked list of ioctl extensions without bounds checking. An attacker can construct a self-referential extension (where ext->next points back to itself) with both in_sync_count and out_sync_count set to zero. The existing guard that checks for non-zero counts fails to trigger because v3d_get_multisync_post_deps() returns immediately when the count is zero, never updating the extension fields. This allows the kernel to loop indefinitely while processing the same extension. The fix rejects any multisync extension where both synchronization counts are zero, returning -EINVAL and preventing the infinite loop condition.

Business impact

This vulnerability enables local denial-of-service attacks that can freeze individual user processes or threads by consuming full CPU cores indefinitely. On multi-user systems, an unprivileged attacker can disrupt service availability for other users or applications. Systems with GPU workloads (graphics, compute) relying on the v3d driver are particularly affected, as hung processes may also prevent resource cleanup and accumulate over time if exploited repeatedly.

Affected systems

The Linux kernel, specifically systems with the DRM v3d (VideoCore V3D) driver enabled. This affects Raspberry Pi and similar devices using VideoCore V3D GPUs, as well as any Linux systems configured with v3d driver support. Affected versions are those prior to the patch resolving this issue; consult vendor advisories and kernel.org for exact version boundaries.

Exploitability

Exploitability is straightforward for local users. No kernel code execution or privilege escalation is required—only the ability to submit an ioctl system call to the v3d device, typically available to any user with read-write access to /dev/dri/card* or similar device nodes. The attack requires no special race conditions or timing; a single crafted syscall triggers the hang. Unprivileged users on systems where GPU device access is broadly permitted face particular risk.

Remediation

Apply kernel patches that add explicit validation to reject multisync extensions with zero in_sync_count and out_sync_count in the v3d_get_multisync_submit_deps() function. Update to a patched kernel version once available from your distribution or kernel.org. Administrators should prioritize systems with v3d driver enabled and shared GPU access policies.

Patch guidance

Monitor your Linux distribution's security advisories for kernel updates addressing CVE-2026-46314. The fix is surgical—a simple validation check added to v3d_get_multisync_submit_deps()—so patched versions should be safe to deploy without extensive compatibility testing. Verify patch status against your kernel source or distribution release notes before deployment.

Detection guidance

Monitor system logs and kernel debug output for signs of CPU saturation caused by hung kernel tasks in the v3d subsystem. Tools like 'dmesg', 'sysstat', and 'perf' can identify runaway kernel threads. Process monitoring for high CPU utilization tied to GPU ioctl calls may indicate exploitation attempts. Network-isolated systems or those without v3d driver loaded are not vulnerable and do not require monitoring.

Why prioritize this

Although this is a local denial-of-service with medium CVSS (5.5), it merits prompt attention because: (1) exploitation is trivial and requires no privilege escalation, (2) it completely freezes affected processes, disrupting availability, (3) systems with shared GPU access face elevated risk, and (4) the fix is straightforward and low-risk to deploy. Prioritize systems with v3d enabled and multi-user access policies.

Risk score, explained

CVSS 5.5 (Medium) reflects a local-only attack vector, lack of confidentiality or integrity impact, and the requirement for user-level privileges. However, the ease of exploitation and the severity of the denial-of-service (complete process hang) mean this should not be treated as low-priority; context-aware prioritization is needed based on your device inventory and GPU driver exposure.

Frequently asked questions