CVE-2025-37797

7.8 HIGH

Denial of Service

📋 TL;DR

This CVE describes a Use-After-Free vulnerability in the Linux kernel's HFSC (Hierarchical Fair Service Curve) queuing discipline scheduler. The vulnerability allows local attackers to potentially crash the kernel or execute arbitrary code by exploiting a race condition in class handling. Systems running affected Linux kernel versions with HFSC qdisc configured are vulnerable.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not explicitly stated in CVE description, but references indicate multiple stable kernel versions are affected.

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when HFSC qdisc is configured and in use. Many systems may not use HFSC by default.

📦 What is this software?

Debian Linux by Debian

View all CVEs affecting Debian Linux →

Linux Kernel by Linux

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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...

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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...

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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 →

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 leading to system crash, or potential privilege escalation to kernel-level code execution allowing complete system compromise.

🟠

Likely Case

Kernel crash causing denial of service, system instability, or potential information disclosure through memory corruption.

🟢

If Mitigated

Limited impact if HFSC qdisc is not in use or if proper kernel hardening measures are implemented.

🌐 Internet-Facing: LOW - This is a local kernel vulnerability requiring local access to exploit.

🏢 Internal Only: MEDIUM - Internal users with local access could exploit this to cause system instability or potentially escalate privileges.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires local access and knowledge of HFSC configuration. The race condition nature makes reliable exploitation challenging.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions containing commits: 20d584a33e480ae80d105f43e0e7b56784da41b9, 28b09a067831f7317c3841812276022d6c940677, 39b9095dd3b55d9b2743df038c32138efa34a9de, 3aa852e3605000d5c47035c3fc3a986d14ccfa9f, 3df275ef0a6ae181e8428a6589ef5d5231e58b5c

Vendor Advisory: https://git.kernel.org/stable/c/20d584a33e480ae80d105f43e0e7b56784da41b9

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution's repositories. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.

🔧 Temporary Workarounds

Disable HFSC qdisc

linux

Remove or disable HFSC queuing discipline configuration if not required.

# Check current qdisc configuration
tc qdisc show
# Remove HFSC qdisc if present
tc qdisc del dev <interface> root hfsc

🧯 If You Can't Patch

Disable HFSC qdisc configuration on all network interfaces
Implement strict access controls to limit local user privileges and prevent unauthorized users from manipulating network queuing

🔍 How to Verify

Check if Vulnerable:

Check if HFSC qdisc is configured: 'tc qdisc show | grep hfsc'. If present and kernel version is unpatched, system is vulnerable.

Check Version:

uname -r

Verify Fix Applied:

Check kernel version includes the fix commits: 'uname -r' and verify with distribution's security advisories. Also verify HFSC qdisc works without issues.

📡 Detection & Monitoring

Log Indicators:

Kernel panic logs
OOPs messages related to net_sched or HFSC
System crash/reboot events

Network Indicators:

Sudden network performance degradation on interfaces using HFSC

SIEM Query:

EventID=41 OR (Source="kernel" AND Message="*HFSC*" OR "*net_sched*")

📊 Metadata

CVE ID: CVE-2025-37797

CVSS v3 Score: 7.8 (HIGH)

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

CWE: CWE-416

EPSS Score: 0.03% exploit probability (8.3th percentile)

Published: May 2, 2025

Last Updated: November 6, 2025

🔗 References

https://git.kernel.org/stable/c/20d584a33e480ae80d105f43e0e7b56784da41b9 Patch
https://git.kernel.org/stable/c/28b09a067831f7317c3841812276022d6c940677 Patch
https://git.kernel.org/stable/c/39b9095dd3b55d9b2743df038c32138efa34a9de Patch
https://git.kernel.org/stable/c/3aa852e3605000d5c47035c3fc3a986d14ccfa9f Patch
https://git.kernel.org/stable/c/3df275ef0a6ae181e8428a6589ef5d5231e58b5c Patch
https://git.kernel.org/stable/c/86cd4641c713455a4f1c8e54c370c598c2b1cee0 Patch
https://git.kernel.org/stable/c/bb583c88d23b72d8d16453d24856c99bd93dadf5 Patch
https://git.kernel.org/stable/c/fcc8ede663569c704fb00a702973bd6c00373283 Patch
https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html Mailing List,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html Mailing List,Third Party Advisory