CVE-2026-53295: Linux Kernel Use-After-Free Vulnerability

CVE-2026-53295 Overview

CVE-2026-53295 is a null pointer dereference vulnerability in the Linux kernel mailbox subsystem. The flaw exists in the mailbox controller code path, where the kernel dereferences the channel array without first verifying that it is attached to the controller. When no channel array is present, the subsequent dereference triggers a kernel OOPS. The issue is compounded by the fact that mailbox controllers can instantiate very early during boot, which may prevent the resulting OOPS from being observed on the console.

The upstream fix adds a sanity check so the kernel fails gracefully when the channel array is missing, rather than proceeding to an unsafe dereference.

Critical Impact
A missing channel array on a mailbox controller can trigger a kernel OOPS during early boot, resulting in denial of service on affected Linux systems.

Affected Products

Linux kernel (mailbox subsystem) — multiple stable branches, per the upstream commit references
Distributions shipping kernels that include the vulnerable mailbox controller code prior to the fix
Embedded and SoC platforms that rely on mailbox controllers for inter-processor communication

Discovery Timeline

2026-06-26 - CVE-2026-53295 published to NVD
2026-06-30 - Last updated in NVD database

Technical Details for CVE-2026-53295

Vulnerability Analysis

The Linux kernel mailbox framework manages communication channels between processors, typically on SoC platforms. Each mailbox controller registers a set of channels that clients can request and use for message passing. The framework code accesses the controller's channel array during channel lookup and initialization.

Before the fix, the code assumed the channel array was always present on a registered controller. When a controller registered without attaching a channel array, subsequent access dereferenced a null or invalid pointer. This produced a kernel OOPS. Because mailbox controllers can be probed very early during system startup, the OOPS could occur before console output is fully initialized, making the failure difficult to diagnose.

The patch adds an explicit sanity check to return an error and fail gracefully when the channel array is absent. The patch also removes a redundant comment. This is classified as a null pointer dereference [CWE-476] leading to denial of service.

Root Cause

The root cause is missing input validation on the controller structure. The mailbox core dereferenced the channel array pointer without confirming it was non-null. Any code path or driver that registered a mailbox controller without populating the channel array would trigger the fault.

Attack Vector

This vulnerability is not remotely exploitable. It manifests when a mailbox controller driver registers a controller without a channel array. The impact is limited to a kernel crash on affected systems, typically at boot time. There is no public evidence of exploitation, and the EPSS score reflects a low likelihood of weaponization.

No verified proof-of-concept code is available. See the upstream commit references for the exact patch content: Kernel Commit 14aed0d and Kernel Commit 3779209.

Detection Methods for CVE-2026-53295

Indicators of Compromise

Kernel OOPS messages referencing the mailbox subsystem in dmesg or serial console logs during early boot
Boot failures or hangs on platforms that use mailbox controllers for inter-processor communication
Stack traces containing symbols from drivers/mailbox/mailbox.c such as mbox_request_channel or of_mbox_index_xlate

Detection Strategies

Inventory running kernel versions across the fleet and compare against the fixed commits listed in the upstream references
Review boot logs from embedded and SoC-based systems for mailbox-related kernel faults
Track driver changes that register mailbox controllers to ensure the channel array is populated before registration

Monitoring Recommendations

Collect and centralize kernel logs from Linux endpoints and embedded devices to surface OOPS events
Alert on repeated boot failures on the same hardware model, which may indicate a driver defect in the mailbox path
Track vendor kernel advisories and stable tree updates for backports of the upstream fix

How to Mitigate CVE-2026-53295

Immediate Actions Required

Apply the upstream Linux kernel patch or the vendor-provided backport that adds the channel array sanity check
Rebuild and redeploy custom kernels for embedded platforms after incorporating the fix
Validate that all in-tree and out-of-tree mailbox controller drivers populate the channel array before calling the registration API

Patch Information

The fix is available in multiple stable branches. Reference commits include 0f11444, 14aed0d, 3779209, 5cc3300, 6362c4a, 9dd7489, c1aad75, and d44872a. Consumers of long-term-support kernels should pull the corresponding stable release that includes the sanity check.

Workarounds

Audit downstream drivers to ensure chans is initialized before mbox_controller_register() is called
Disable or unload mailbox controller drivers that are not required on the target platform, where feasible
Delay non-essential driver initialization until after core mailbox subsystem stability can be verified in test environments

bash

# Verify running kernel version and check for mailbox subsystem errors
uname -r
dmesg | grep -i -E 'mailbox|mbox|Oops'

# On systems using a distribution kernel, apply available updates
# Debian/Ubuntu
sudo apt update && sudo apt upgrade linux-image-$(uname -r | cut -d- -f3-)

# RHEL/CentOS/Fedora
sudo dnf update kernel

# Reboot to load the patched kernel
sudo systemctl reboot