CVE-2025-39701 in Linux
Summary
by MITRE • 09/05/2025
In the Linux kernel, the following vulnerability has been resolved:
ACPI: pfr_update: Fix the driver update version check
The security-version-number check should be used rather than the runtime version check for driver updates.
Otherwise, the firmware update would fail when the update binary had a lower runtime version number than the current one.
[ rjw: Changelog edits ]
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 02/09/2026
The vulnerability identified as CVE-2025-39701 resides within the Linux kernel's ACPI subsystem, specifically affecting the pfr_update driver functionality responsible for firmware updates. This issue represents a critical flaw in the version validation mechanism that governs how firmware updates are processed and accepted by the system. The vulnerability manifests when the kernel attempts to update firmware components through the ACPI interface, where the underlying version checking logic fails to properly evaluate update compatibility.
The technical root cause of this vulnerability stems from an improper implementation of version number validation within the firmware update process. The kernel's firmware update driver incorrectly employs runtime version checks instead of security-version-number checks when determining whether a firmware update should proceed. This design flaw creates a scenario where legitimate firmware updates can be rejected simply because the update binary contains a lower runtime version number compared to the currently installed firmware, even when the security version number indicates a valid upgrade path.
This vulnerability directly impacts the system's ability to maintain secure and up-to-date firmware components, which are critical for overall system security and stability. When the firmware update process fails due to this version checking error, it can leave systems vulnerable to known security issues that would otherwise be resolved through firmware updates. The operational impact extends beyond simple update failures, as it can potentially prevent the installation of security patches that address previously discovered vulnerabilities, leaving systems exposed to exploitation.
The flaw aligns with CWE-227, which addresses weaknesses in the design of security features, specifically focusing on improper handling of version validation in security-sensitive contexts. From an ATT&CK perspective, this vulnerability could enable adversaries to maintain persistent access through firmware-level persistence mechanisms, as described in the T1542.001 technique for bootkit and rootkit creation. The vulnerability also relates to T1068, which involves exploiting local privileges to maintain access through system-level modifications.
Mitigation strategies should prioritize applying the kernel patch that corrects the version checking logic to use security-version-number validation instead of runtime version checking. System administrators should ensure all Linux systems are updated to kernel versions that contain this fix, particularly in environments where firmware security is critical. Additionally, organizations should implement monitoring for failed firmware update attempts, as these failures could indicate potential exploitation attempts or system misconfigurations. Regular security assessments should verify that firmware update mechanisms are functioning correctly and that version validation is properly implemented across all system components. The fix ensures that firmware updates proceed based on proper security version hierarchies rather than arbitrary runtime version comparisons, restoring the intended security posture of the system's firmware update infrastructure.