CVE-2025-39701
📋 TL;DR
This CVE describes a vulnerability in the Linux kernel's ACPI Platform Firmware Runtime Update (pfr_update) driver where the wrong version check is used during driver updates. This could allow malicious firmware updates to bypass security checks, potentially leading to system compromise. It affects Linux systems with ACPI firmware update capabilities.
💻 Affected Systems
- Linux kernel
📦 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 →⚠️ Risk & Real-World Impact
Worst Case
An attacker with local access could install malicious firmware updates that bypass security checks, potentially leading to persistent rootkit installation, system takeover, or hardware-level compromise.
Likely Case
Malicious firmware updates could be installed by local attackers, leading to privilege escalation, persistence mechanisms, or system instability.
If Mitigated
With proper access controls and firmware validation, the impact is limited to denial of service from failed updates or system instability.
🎯 Exploit Status
Exploitation requires local access and ability to trigger firmware updates. The vulnerability is in version checking logic, not a direct code execution flaw.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check kernel commits: 79300ff532bccbbf654992c7c0863b49a6c3973c, 8151320c747efb22d30b035af989fed0d502176e, 908094681f645d3a78e18ef90561a97029e2df7b, b00219888c11519ef75d988fa8a780da68ff568e, cf0a88124e357bffda487cbf3cb612bb97eb97e4
Vendor Advisory: https://git.kernel.org/stable/c/79300ff532bccbbf654992c7c0863b49a6c3973c
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing the fix commits. 2. Check with your distribution vendor for patched kernel packages. 3. Reboot system after kernel update.
🔧 Temporary Workarounds
Restrict firmware update permissions
linuxLimit access to firmware update functionality to privileged users only
chmod 600 /sys/firmware/acpi/pfr_update
setfacl -m u:root:rw /sys/firmware/acpi/pfr_update
Disable ACPI firmware updates if not needed
linuxPrevent firmware updates through kernel module blacklisting or boot parameters
echo 'blacklist pfr_update' >> /etc/modprobe.d/blacklist.conf
Add 'acpi.pfr_update=0' to kernel boot parameters
🧯 If You Can't Patch
- Implement strict access controls on firmware update interfaces
- Monitor for unauthorized firmware update attempts and system changes
🔍 How to Verify
Check if Vulnerable:
Check if pfr_update driver is loaded and accessible: lsmod | grep pfr_update and check /sys/firmware/acpi/pfr_update permissionsCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes fix commits: uname -r and check kernel changelog for commit hashes📡 Detection & Monitoring
Log Indicators:
- Unexpected firmware update attempts in kernel logs
- ACPI firmware update errors or warnings
- Unauthorized access to /sys/firmware/acpi/pfr_update
Network Indicators:
- None - this is a local vulnerability
SIEM Query:
source="kernel" AND ("pfr_update" OR "firmware update" OR "ACPI update")🔗 References
- https://git.kernel.org/stable/c/79300ff532bccbbf654992c7c0863b49a6c3973c
- https://git.kernel.org/stable/c/8151320c747efb22d30b035af989fed0d502176e
- https://git.kernel.org/stable/c/908094681f645d3a78e18ef90561a97029e2df7b
- https://git.kernel.org/stable/c/b00219888c11519ef75d988fa8a780da68ff568e
- https://git.kernel.org/stable/c/cf0a88124e357bffda487cbf3cb612bb97eb97e4
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
