CVE-2026-53019

What it actually does

This flaw is a Linux kernel denial-of-service issue in the Spacemit clock control unit driver. An inverted condition in ccu_mix_trigger_fc() can prevent the required frequency-change trigger from being issued during CPU frequency scaling. On affected systems using the Spacemit CCU/cpufreq path, normal or attacker-induced CPU frequency transitions can leave clock state inconsistent and lead to a kernel panic, reboot, or system hang. The impact is availability-focused; there is no indication from the provided data that it enables privilege escalation, data disclosure, or arbitrary code execution.

Why it matters to the business

Affected Linux systems may crash or reboot when CPU frequency scaling occurs, causing service outages, interrupted workloads, device instability, and potential loss of unsaved in-memory state. Risk is highest for systems built on affected Spacemit platforms where power management or dynamic CPU frequency scaling is enabled. This is not currently listed in CISA KEV, has no known exploit maturity, and has a very low EPSS score, so broad active exploitation is not indicated; however, availability-sensitive embedded, edge, appliance, or server deployments should still prioritize remediation during normal kernel maintenance cycles.

How an attack unfolds

An attacker would need a way to cause repeated CPU frequency transitions on an affected Linux system using the vulnerable Spacemit clock/cpufreq driver path. In a local scenario, the attacker could generate bursty CPU load, repeatedly change power-management state where permitted, or interact with cpufreq sysfs controls if they have sufficient privileges. In a remote-but-indirect scenario, an attacker may attempt to drive high and variable CPU utilization through an exposed application or network service, relying on the CPU frequency governor to scale frequencies. When the vulnerable code path is exercised, the incorrect condition can skip the frequency-change trigger, causing unstable clock state and potentially resulting in a kernel panic or system reboot. There is no evidence in the provided data of a public exploit or known threat actor use.

How to fix it

Update to a Linux kernel version that includes the upstream fix for the Spacemit ccu_mix frequency-change trigger condition. Because no exact affected product list or fixed package versions were provided, use vendor kernel advisories, distribution security notices, BSP releases, or appliance firmware updates to identify the corrected kernel build for each affected platform. Where immediate patching is not possible, reduce exposure by disabling or constraining dynamic CPU frequency scaling where operationally acceptable, using a stable/fixed CPU frequency governor, limiting untrusted local shell access, and rate-limiting externally reachable services that can be abused to generate sustained CPU-load oscillation. Validate mitigations carefully, as changing CPU power-management settings may affect performance, thermals, and battery life.

How to confirm the fix worked

Confirm the running kernel or firmware contains the fix for the Spacemit ccu_mix_trigger_fc() condition. On source-based or internally maintained kernels, verify the corrected clk/spacemit ccu_mix driver code is present and that the frequency-change trigger is no longer skipped due to the inverted condition. On packaged systems, compare the installed kernel package, firmware, or BSP version against the vendor’s fixed release. Runtime validation should include controlled CPU frequency scaling tests under expected governors while monitoring for kernel warnings, lockups, panics, and unexpected reboots. Also verify whether the platform actually uses the affected Spacemit clock/cpufreq driver path; systems not using that hardware/driver combination are unlikely to be exposed.

Typical attack path

1. Identify or reach a Linux system running an affected kernel on hardware that uses the Spacemit CCU/cpufreq driver path.
2. Create conditions that cause CPU frequency changes, such as bursty CPU load, repeated workload spikes, or power-management changes.
3. If local privileges allow it, interact with cpufreq controls under /sys/devices/system/cpu/ to force or accelerate frequency transitions.
4. Trigger the vulnerable frequency-change path in ccu_mix_trigger_fc().
5. Cause a kernel panic, system hang, reboot, or service interruption.

How to detect it

Look for evidence of prior exploitation or triggering by reviewing kernel logs, persistent journal logs, console logs, watchdog logs, crash dumps, and platform management logs for panics or reboots occurring during CPU frequency changes. Relevant sources include dmesg output, /var/log/kern.log, /var/log/messages, /var/log/syslog, journalctl -k, pstore/ramoops records, kdump/vmcore artifacts, BMC or device-management event logs, and application logs showing sudden termination at the same time as a kernel crash. Search for cpufreq, clk, ccu, spacemit, frequency scaling, watchdog reset, soft lockup, hard lockup, kernel panic, and unexpected reboot messages. Correlate crash times with workload spikes, power-management changes, governor changes, or writes to cpufreq sysfs paths. Absence of these artifacts does not prove the system was unaffected, especially if logs are volatile or overwritten after reboot.

• ccu_mix_trigger_fc
• spacemit
• cpufreq
• frequency change
• frequency scaling
• scaling_governor
• scaling_setspeed
• /sys/devices/system/cpu/cpu*/cpufreq/
• Kernel panic
• kernel panic - not syncing
• Oops:
• BUG: kernel NULL pointer dereference
• watchdog: BUG: soft lockup
• watchdog: Watchdog detected hard LOCKUP
• rcu: INFO: rcu_sched detected stalls
• pstore
• ramoops
• vmcore
• /proc/vmcore
• /var/crash/
• /sys/fs/pstore/
• clk: spacemit
• ccu_mix

What your security team should do

• Inventory Linux systems, appliances, and embedded devices using Spacemit-based kernels or board support packages.
• Prioritize patching for availability-sensitive devices, remotely managed edge systems, and systems with untrusted local users or internet-facing services that can be used to induce CPU load.
• Obtain fixed kernels or firmware from the operating system, hardware, BSP, or appliance vendor and schedule deployment through normal maintenance windows.
• If patching is delayed, consider temporarily using a fixed-performance CPU governor or disabling dynamic frequency scaling where operationally safe.
• Monitor for unexplained kernel panics, spontaneous reboots, watchdog resets, and cpufreq/clock-related kernel messages on potentially affected devices.
• Because this is not KEV-listed and has low EPSS with no known exploit maturity, treat it as a stability and availability risk rather than an emergency internet-scale exploitation event unless local exposure or business criticality increases urgency.