CVE-2025-39813 – This CVE describes a race condition in the Linu... (How to Fix)

Q: What is the severity of CVE-2025-39813?

CVE-2025-39813 has a CVSS score of 4.7 (MEDIUM). This CVE describes a race condition in the Linux kernel's ftrace subsystem that can trigger a kernel warning when ftrace_dump is called concurrently with reading trace_pipe. The vulnerability affects Linux systems with ftrace enabled and could potentially be used to cause kernel instability or denial of service.

📋 TL;DR

This CVE describes a race condition in the Linux kernel's ftrace subsystem that can trigger a kernel warning when ftrace_dump is called concurrently with reading trace_pipe. The vulnerability affects Linux systems with ftrace enabled and could potentially be used to cause kernel instability or denial of service.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not explicitly stated in CVE; likely affects multiple stable kernel versions before the fix commits.

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Requires ftrace to be enabled and configured; not all Linux systems have ftrace enabled by default.

📦 What is this software?

Debian Linux by Debian

View all CVEs affecting Debian Linux →

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 →

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

Kernel panic or system crash if the warning triggers additional issues in a production environment, leading to denial of service.

🟠

Likely Case

Kernel warning messages in system logs and potential minor system instability during concurrent ftrace operations.

🟢

If Mitigated

No impact if ftrace is disabled or the system is patched; warning messages only in logs if triggered.

🌐 Internet-Facing: LOW - This vulnerability requires local access to trigger and is not directly exploitable over the network.

🏢 Internal Only: MEDIUM - Local users with appropriate permissions could trigger the warning, potentially affecting system stability in multi-user environments.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires local access and specific timing conditions to trigger the race condition.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions containing the fix commits referenced in the CVE

Vendor Advisory: https://git.kernel.org/stable/c/28c8fb7ae2ad27d81c8de3c4fe608c509f6a18aa

Restart Required: Yes

Instructions:

1. Update Linux kernel to a version containing the fix commits. 2. Reboot system to load new kernel. 3. Verify ftrace functionality works without warnings.

🔧 Temporary Workarounds

Disable ftrace

all

Disable the ftrace subsystem to prevent the race condition from being triggered.

echo 0 > /sys/kernel/debug/tracing/tracing_on
echo nop > /sys/kernel/debug/tracing/current_tracer

Restrict access to trace_pipe

all

Limit access to /sys/kernel/tracing/trace_pipe to prevent concurrent reading during ftrace_dump operations.

chmod 600 /sys/kernel/tracing/trace_pipe
chown root:root /sys/kernel/tracing/trace_pipe

🧯 If You Can't Patch

Monitor system logs for kernel warnings related to ftrace and investigate any occurrences.
Implement strict access controls to prevent unauthorized users from accessing ftrace functionality.

🔍 How to Verify

Check if Vulnerable:

Check if ftrace is enabled and test concurrent access to trace_pipe during ftrace_dump operations while monitoring dmesg for warnings.

Check Version:

uname -r

Verify Fix Applied:

After patching, attempt to reproduce the race condition by running concurrent ftrace operations and verify no warnings appear in kernel logs.

📡 Detection & Monitoring

Log Indicators:

Kernel warning messages containing 'WARN_ON_ONCE' and 'trace_printk_seq' in dmesg or /var/log/kern.log

Network Indicators:

None - this is a local vulnerability

SIEM Query:

source="kernel" AND "WARN_ON_ONCE" AND "trace_printk_seq"

📊 Metadata

CVE ID: CVE-2025-39813

CVSS v3 Score: 4.7 (MEDIUM)

CVSS Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

CWE: CWE-362

EPSS Score: 0.01% exploit probability (0.6th percentile)

Published: September 16, 2025

Last Updated: January 16, 2026

🔗 References

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