CVE-2025-71106: Linux Kernel Privilege Escalation Flaw

CVE-2025-71106 Overview

A logic error vulnerability has been identified in the Linux kernel's power management subsystem, specifically within the filesystems_freeze_callback() function. The vulnerability stems from a reversed boolean check introduced by commit a3f8f8662771 ("power: always freeze efivarfs"), which causes unintended behavior where all file systems are frozen when filesystem_freeze_enabled is set to false.

This improper conditional logic can trigger the WARN_ON_ONCE() assertion in __set_task_frozen(), likely due to attempts to freeze file systems that are not properly prepared for the freeze operation. The fix involves adding a logical negation to correct the reversed check.

Critical Impact

Improper filesystem freezing behavior during power management operations can lead to system instability, kernel warnings, and potential denial of service conditions on affected Linux systems.

Affected Products

• Linux kernel with commit a3f8f8662771 applied
• Linux kernel versions with the faulty filesystems_freeze_callback() implementation
• Systems utilizing power management with filesystem freeze functionality

Discovery Timeline

• 2026-01-14 - CVE CVE-2025-71106 published to NVD
• 2026-01-14 - Last updated in NVD database

Technical Details for CVE-2025-71106

Vulnerability Analysis

The vulnerability exists in the filesystems_freeze_callback() function within the Linux kernel's power management (PM) code. When commit a3f8f8662771 was introduced to ensure efivarfs is always frozen during power transitions, it inadvertently introduced a reversed conditional check on the freeze_all_ptr pointer.

The logic error causes the filesystem freeze mechanism to behave contrary to the intended design: when filesystem_freeze_enabled is false (indicating filesystem freezing should be disabled), the code incorrectly proceeds to freeze all filesystems anyway. This inverted behavior can result in filesystem freeze operations being attempted on systems or filesystems that are not configured or ready for such operations.

The consequence of this logic error manifests as WARN_ON_ONCE() assertions being triggered in __set_task_frozen(). These warnings indicate that the kernel is attempting to freeze tasks associated with filesystems that have not been properly prepared, potentially leading to system instability during power management transitions such as suspend or hibernate operations.

Root Cause

The root cause is a simple but impactful logic error in the boolean conditional check within filesystems_freeze_callback(). The freeze_all_ptr check was implemented without the necessary logical negation, resulting in the conditional evaluating to the opposite of what was intended. This type of error is a common programming mistake that can have significant consequences in kernel-level code where correct control flow is critical for system stability.

Attack Vector

This vulnerability is primarily triggered through legitimate system operations rather than external attack vectors. The issue manifests when:

1. The system initiates a power management transition (suspend, hibernate, or similar PM operation)
2. The filesystems_freeze_callback() function is invoked as part of the PM sequence
3. The reversed logic causes inappropriate filesystem freeze operations
4. Kernel warnings are triggered when attempting to freeze unprepared filesystems

While this vulnerability does not appear to be directly exploitable for privilege escalation or code execution, it can cause system instability and denial of service conditions during normal power management operations.

Detection Methods for CVE-2025-71106

Indicators of Compromise

• Kernel log messages containing WARN_ON_ONCE() assertions from __set_task_frozen()
• Unexpected filesystem freeze operations during power management transitions
• System instability or hang conditions during suspend/hibernate operations
• Kernel warnings referencing filesystems_freeze_callback() in stack traces

Detection Strategies

• Monitor kernel logs (dmesg or /var/log/kern.log) for warning messages related to filesystem freeze operations
• Implement alerting on kernel warning patterns matching __set_task_frozen or filesystems_freeze_callback
• Review system behavior during power management transitions for unexpected hangs or delays
• Use kernel tracing tools (ftrace, perf) to monitor filesystem freeze callback execution

Monitoring Recommendations

• Configure centralized logging to capture kernel warnings and stack traces
• Establish baseline behavior for power management operations on affected systems
• Implement automated monitoring for kernel oops and warning messages
• Test suspend/hibernate functionality in controlled environments before deploying patches

How to Mitigate CVE-2025-71106

Immediate Actions Required

• Apply the kernel patches from the stable kernel tree immediately
• Review and test power management functionality after patching
• Monitor system logs for any remaining warnings during PM operations
• Consider temporarily disabling automatic suspend/hibernate on critical systems until patched

Patch Information

The Linux kernel maintainers have released patches to address this vulnerability. The fix adds the missing logical negation to the freeze_all_ptr check in filesystems_freeze_callback(), restoring the intended behavior where filesystem freeze operations only occur when filesystem_freeze_enabled is true.

The patches are available through the following kernel git commits:

• Kernel Git Commit 222047f
• Kernel Git Commit b107196

System administrators should update to kernel versions containing these fixes through their distribution's package management system.

Workarounds

• Disable automatic power management (suspend/hibernate) features on affected systems as a temporary measure
• Avoid manual suspend/hibernate operations until patches are applied
• Monitor systems closely for kernel warnings if patches cannot be immediately applied
• Consider running systems with filesystem_freeze_enabled set to true if supported, to match the inverted logic behavior

# Check kernel version and review available updates
uname -r
# For Debian/Ubuntu systems
apt update && apt list --upgradable | grep linux
# For RHEL/CentOS systems
yum check-update kernel
# Monitor kernel logs for related warnings
dmesg | grep -i "freeze\|__set_task_frozen"