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The CVE-2025-39859 vulnerability is a use-after-free race condition within the `ptp_ocp` driver of the Linux kernel. The flaw exists in the `ptp_ocp_detach()` function, which is responsible for cleaning up when a Precision Time Protocol (PTP) OCP device is removed. This function incorrectly only called `timer_delete_sync()` to deactivate a watchdog timer if the timer was in a pending state. If the timer’s handler function, ptp_ocp_watchdog(), was already executing on another CPU thread, the cleanup logic would proceed without waiting for it to finish. This created a critical race window. The kernel could then proceed to free the parent `devlink` object containing the `ptp_ocp` structure while the concurrently running timer handler still held a pointer to it. The handler would then attempt to access the already-freed memory (the `bp` pointer), leading to a use-after-free error. This corrupts kernel memory and typically results in a system crash or kernel panic, compromising availability. The fix is to unconditionally call `timer_delete_sync()` in ptp_ocp_detach(), ensuring the timer handler is never running when its parent data structures are deallocated.
Platform:
Linux Kernel
Version:
Various versions
Vulnerability :
Use-After-Free
Severity:
HIGH
date:
2025-09-19
Prediction:
2026-01-31
What Undercode Say
Analytics
Check if PTP subsystem is present in your kernel configuration.
grep -i ptp /boot/config-$(uname -r)
Identify the exact running kernel version.
uname -a
Locate PTP device interfaces in sysfs.
ls /sys/class/ptp
Check for the vulnerable code commits in the kernel source.
git log --oneline --grep="f10d3c7267ac" --grep="8bf935cf7898"
Verify if the `ptp_ocp` kernel module is loaded.
lsmod | grep ptp_ocp
How Exploit
Prerequisites: Local access with low privileges (PR:L). A kernel compiled with the vulnerable PTP OCP driver.
Mechanism: An attacker triggers the race condition by causing the `ptp_ocp` device to be detached (e.g., via device removal) while its watchdog timer is active. This requires access to relevant device or sysfs interfaces.
Result: Successful exploitation corrupts kernel memory, leading to a system crash, denial of service, or potential privilege escalation. No reliable public proof-of-concept for code execution is known.
Protection from this CVE
Update the Linux kernel to a version containing the fixes. Key fix commits are `f10d3c7267ac` and 8bf935cf7898.
Verify the patch is included by checking your distribution’s kernel changelog for these commit IDs.
For immediate mitigation where patching is not possible, restrict local user access to PTP-related sysfs interfaces if feasible.
Impact
Primary Impact: System instability, kernel panic, and denial of service (availability loss).
Security Impact: The CVSS 3.1 score of 7.8 (HIGH) indicates high impacts on Confidentiality, Integrity, and Availability (C:H/I:H/A:H). While use-after-free flaws can theoretically lead to privilege escalation, this requires further exploitation and is not proven for this specific bug.
Scope: Affects kernels from version 5.15 up to versions before 6.16.6 and 6.17.
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Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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