CVE-2026-53024: Linux Greybus Use-After-Free Kernel Panic Vulnerability

Technical summary

CVE-2026-53024 is a use-after-free (CWE-416) flaw in the Greybus subsystem's raw driver (gb_raw). The vulnerability occurs because the disconnect function calls gb_connection_destroy, which frees the connection object, while the write file operation (raw_write) may simultaneously invoke gb_operation_sync with that now-freed connection pointer. This leads to a NULL pointer dereference or memory corruption when gb_operation_create_common attempts to access fields within the freed connection structure. The kernel panic manifests with CONFIG_INIT_ON_FREE_DEFAULT_ON enabled, though the underlying race condition exists regardless. The fix introduces a read-write lock to serialize access: write operations acquire a read lock, disconnect acquires a write lock, ensuring write cannot proceed during or after disconnection.

Business impact

For Linux distributions and embedded systems using Greybus (primarily used in mobile and IoT devices with modular hardware), this vulnerability permits a local, unprivileged user to trigger a kernel panic and cause denial of service. The attack requires only write access to the character device, a capability typically available to unprivileged users on systems where the device is exposed. This can interrupt critical services, cause data loss from unclean shutdown, and potentially be chained with other vulnerabilities for privilege escalation. Organizations deploying Greybus-based hardware should evaluate the operational impact of kernel crashes on their infrastructure.

Affected systems

The Linux kernel is affected, specifically builds that include the Greybus raw driver module (gb_raw). Vulnerability manifestation requires: (1) the Greybus subsystem to be compiled into or loaded as a module, (2) a Greybus device or bundle that exposes a raw character device, and (3) a local user with permission to write to that device node. Typical environments include Linux phones, tablets, modular hardware platforms, and embedded systems using Greybus for device communication. Desktop and server distributions may have Greybus disabled by default, reducing exposure.

Exploitability

Exploitability is straightforward from a technical perspective: triggering the vulnerability requires only a write() system call to the character device after disconnect occurs. However, real-world exploitation difficulty depends on whether the Greybus subsystem and raw driver are enabled and whether the target device node has permissive ownership or group membership. The CVSS 3.1 score of 7.8 (HIGH) reflects local access requirement (AV:L), low attack complexity (AC:L), and low privilege requirement (PR:L), with high impact across confidentiality, integrity, and availability. The vulnerability is not tracked as actively exploited (KEV status: not listed), but local DoS vulns in ubiquitous kernel subsystems typically see proof-of-concept development rapidly.

Remediation

A kernel patch has been released that adds read-write lock synchronization between the write path and disconnect path. The lock ensures that ongoing write operations complete before connection destruction, and new write attempts are rejected or blocked during disconnect. To remediate, apply the kernel patch or update to a patched kernel version released after 2026-07-15 (the last modification date). Verify against the vendor (kernel.org) advisory and your distribution's security advisories for specific patched versions. Until patched, restrict write access to the raw character device to trusted users only.

Patch guidance

Obtain the patched Linux kernel from your distribution's security update channel or from kernel.org. The vulnerability was resolved in the mainline kernel; stable and LTS branches will receive backports. When patching, ensure you are updating to a kernel version released on or after the modification date (2026-07-15) and verify the patch commit addresses the rw lock mechanism in the Greybus raw driver. Test patches in a non-production environment first, as kernel updates require rebooting. If you maintain a custom kernel, apply the upstream patch directly to the affected gb_raw module source.

Detection guidance

Detection at runtime is challenging because the vulnerability manifests as a kernel panic, which generates a crash dump. Monitor kernel logs (dmesg, journalctl) for NULL pointer dereference panics originating from gb_operation_create_common or raw_write. Correlate timing of crash logs with write operations to the Greybus raw device node (typically /dev/gball* or similar). Inspect audit logs for patterns of repeated writes to device nodes followed by system resets. On systems with kdump or kexec configured, kernel crash dumps will provide stack traces for forensic analysis. Proactive detection via static analysis (e.g., checking kernel module compile flags) can identify systems with Greybus enabled.

Why prioritize this

Prioritize patching systems where: (1) Greybus is enabled in the kernel and the raw driver is active, (2) the raw character device is writable by unprivileged users, and (3) system availability is critical (e.g., embedded controllers, always-on devices). The HIGH CVSS score and ease of triggering a local denial of service warrant swift remediation. However, systems where Greybus is disabled or the raw device is not exposed can deprioritize this patch relative to remote code execution vulnerabilities. Embedded Linux systems and mobile devices should treat this as moderate-to-high priority; traditional server and desktop Linux deployments may have lower risk if Greybus is not in use.

Risk score, explained

The CVSS 3.1 score of 7.8 (HIGH) reflects: Attack Vector Local (AV:L) — requires local system access; Attack Complexity Low (AC:L) — no special conditions or timing required beyond a write() call; Privileges Required Low (PR:L) — non-root user with device write permission suffices; User Interaction None (UI:N) — attack is purely programmatic; Scope Unchanged (S:U) — impact limited to the system itself; Confidentiality High, Integrity High, Availability High (C:H/I:H/A:H) — kernel panic can leak memory, corrupt state, and crash the system. The score appropriately penalizes a local DoS with potential for memory disclosure and system instability, though the lack of remote exploitability prevents a critical rating.

Frequently asked questions