CVE-2025-38083 – A race condition in the Linux kernel's PRIO que... (How to Fix)

Q: What is the severity of CVE-2025-38083?

CVE-2025-38083 has a CVSS score of 4.7 (MEDIUM). A race condition in the Linux kernel's PRIO queuing discipline allows an attacker to cause a parent qdisc's packet queue length counter to underflow. This affects Linux systems using the PRIO qdisc with SFQ perturb timer enabled, potentially leading to denial of service or incorrect traffic scheduling.

📋 TL;DR

A race condition in the Linux kernel's PRIO queuing discipline allows an attacker to cause a parent qdisc's packet queue length counter to underflow. This affects Linux systems using the PRIO qdisc with SFQ perturb timer enabled, potentially leading to denial of service or incorrect traffic scheduling.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not specified in CVE, but fix commits indicate stable kernel versions before the fix

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Only affects systems using PRIO qdisc with SFQ perturb timer enabled. Not all Linux systems use this configuration.

📦 What is this software?

Debian Linux by Debian

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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...

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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

Persistent denial of service on affected network interfaces, causing complete network disruption for the system.

🟠

Likely Case

Intermittent network performance degradation or packet loss on interfaces using PRIO qdisc.

🟢

If Mitigated

Minimal impact if systems are patched or don't use PRIO qdisc with SFQ perturb timer.

🌐 Internet-Facing: LOW - Requires local access or ability to manipulate network queuing.

🏢 Internal Only: MEDIUM - Could be exploited by local users or through network manipulation in internal environments.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: HIGH

Exploitation requires precise timing and specific network configuration. Race conditions are difficult to reliably exploit.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions containing commits: 20f68e6a9e41693cb0e55e5b9ebbcb40983a4b8f, 3aaa7c01cf19d9b9bb64b88b65c3a6fd05da2eb4, 4483d8b9127591c60c4eb789d6cab953bc4522a9, 46c15c9d0f65c9ba857d63f53264f4b17e8a715f, 53d11560e957d53ee87a0653d258038ce12361b7

Vendor Advisory: https://git.kernel.org/stable/c/20f68e6a9e41693cb0e55e5b9ebbcb40983a4b8f

Restart Required: Yes

Instructions:

1. Update Linux kernel to version containing the fix commits. 2. Reboot system to load new kernel. 3. Verify kernel version with 'uname -r'.

🔧 Temporary Workarounds

Disable SFQ perturb timer

linux

Disable the SFQ perturb timer in PRIO qdisc configuration to prevent the race condition trigger.

tc qdisc change dev <interface> root prio perturb 0

Use alternative queuing discipline

linux

Replace PRIO qdisc with alternative queuing discipline like HTB or FQ_CODEL.

tc qdisc del dev <interface> root
tc qdisc add dev <interface> root htb

🧯 If You Can't Patch

Implement workaround to disable SFQ perturb timer on all affected interfaces
Monitor network interfaces for abnormal packet loss or queue underflows

🔍 How to Verify

Check if Vulnerable:

Check if system uses PRIO qdisc: 'tc qdisc show | grep prio'. Check kernel version against patched versions.

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version contains fix commits: 'uname -r'. Check git log for commit hashes.

📡 Detection & Monitoring

Log Indicators:

Kernel logs showing qdisc errors or underflows
Network interface statistics showing abnormal packet drops

Network Indicators:

Unexpected network performance degradation on specific interfaces
Increased packet loss on PRIO-configured interfaces

SIEM Query:

source="kernel" AND ("qdisc" OR "prio" OR "underflow")

📊 Metadata

CVE ID: CVE-2025-38083

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: 0.03% exploit probability (6.1th percentile)

Published: June 20, 2025

Last Updated: December 17, 2025

🔗 References

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