CVE-2025-21902
📋 TL;DR
This Linux kernel vulnerability in the UCSI (USB Type-C Connector System Software Interface) ACPI backend causes a spurious warning/assertion splat when polling CCI (Command Status and Control Interface) with notifications disabled. It affects systems using UCSI for USB Type-C management, potentially causing kernel warnings and system instability. The issue occurs during USB Type-C initialization on affected Linux systems.
💻 Affected Systems
- Linux kernel with UCSI ACPI backend support
📦 What is this software?
Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →⚠️ Risk & Real-World Impact
Worst Case
System instability or kernel panic during USB Type-C initialization, potentially causing system crashes or hardware management failures.
Likely Case
Kernel warning messages in system logs during boot or USB Type-C operations, but no actual security compromise.
If Mitigated
Minor system log noise with no functional impact after proper patching.
🎯 Exploit Status
This appears to be a stability/assertion issue rather than a traditional security vulnerability. No evidence of remote exploitation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in kernel commits: 012b98cdb54c7d47743ee7fc402fa23f2d90529a, 1aec5c9066965ac0984e385bbc31455ae31cbffc, 976e7e9bdc7719a023a4ecccd2e3daec9ab20a40
Vendor Advisory: https://git.kernel.org/stable/c/012b98cdb54c7d47743ee7fc402fa23f2d90529a
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing the fix commits. 2. Check with your distribution for backported patches. 3. Reboot system after kernel update.
🔧 Temporary Workarounds
Disable UCSI ACPI backend
linuxPrevent the vulnerable code from being loaded by disabling the UCSI ACPI module
echo 'blacklist ucsi_acpi' >> /etc/modprobe.d/blacklist-ucsi.conf
update-initramfs -u
reboot
🧯 If You Can't Patch
- Monitor system logs for UCSI-related warnings and restart affected services if instability occurs
- Consider disabling USB Type-C features if not required for system operation
🔍 How to Verify
Check if Vulnerable:
Check kernel logs for 'ucsi_reset_ppm' warnings or examine kernel version against patched commitsCheck Version:
uname -r && grep -i 'ucsi' /var/log/kern.logVerify Fix Applied:
Verify kernel version includes the fix commits and monitor logs for absence of UCSI warnings📡 Detection & Monitoring
Log Indicators:
- WARNING: CPU: ... at drivers/usb/typec/ucsi/ucsi.c:1388 ucsi_reset_ppm
- UCSI initialization failures in kernel logs
Network Indicators:
- None - this is a local kernel issue
SIEM Query:
source="kernel" AND "ucsi_reset_ppm" AND "WARNING"