CVE-2025-21680 – This CVE describes an out-of-bounds array acces... (How to Fix)

Q: What is the severity of CVE-2025-21680?

CVE-2025-21680 has a CVSS score of 7.8 (HIGH). This CVE describes an out-of-bounds array access vulnerability in the Linux kernel's pktgen module, specifically in the get_imix_entries function. It allows local attackers with sufficient privileges to cause kernel memory corruption, potentially leading to denial of service or privilege escalation. Affected systems are those running vulnerable Linux kernel versions with pktgen enabled.

📋 TL;DR

This CVE describes an out-of-bounds array access vulnerability in the Linux kernel's pktgen module, specifically in the get_imix_entries function. It allows local attackers with sufficient privileges to cause kernel memory corruption, potentially leading to denial of service or privilege escalation. Affected systems are those running vulnerable Linux kernel versions with pktgen enabled.

💻 Affected Systems

Products:

Linux kernel

Versions: Versions before the fix commits (specific versions vary by distribution; check kernel changelogs for 1a9b65c672ca9dc4ba52ca2fd54329db9580ce29 and related patches).

Operating Systems: Linux-based operating systems (e.g., Ubuntu, Red Hat, Debian, SUSE)

Default Config Vulnerable: ✅ No

Notes: pktgen is a kernel module for packet generation; vulnerability only affects systems where pktgen is loaded and accessible (typically requires root or CAP_NET_ADMIN privileges).

📦 What is this software?

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 →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Kernel panic or crash leading to system instability, or potential privilege escalation to root via memory corruption.

🟠

Likely Case

Local denial of service (system crash or kernel panic) due to invalid memory access.

🟢

If Mitigated

Minimal impact if pktgen is disabled or access is restricted via proper kernel hardening.

🌐 Internet-Facing: LOW, as exploitation requires local access to the system.

🏢 Internal Only: MEDIUM, as internal users with local shell access could exploit this to disrupt services or escalate privileges.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires local access and privileges to interact with pktgen; no known public exploits as of analysis.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Fixed in kernel commits: 1a9b65c672ca9dc4ba52ca2fd54329db9580ce29, 3450092cc2d1c311c5ea92a2486daa2a33520ea5, 76201b5979768500bca362871db66d77cb4c225e, 7cde21f52042aa2e29a654458166b873d2ae66b3, e5d24a7074dcd0c7e76b7e7e4efbbe7418d62486 (backported to stable branches).

Vendor Advisory: https://git.kernel.org/stable/c/1a9b65c672ca9dc4ba52ca2fd54329db9580ce29

Restart Required: Yes

Instructions:

1. Update the Linux kernel to a version containing the fix. 2. For distributions, use package manager (e.g., 'apt update && apt upgrade' for Debian/Ubuntu, 'yum update' for RHEL). 3. Reboot the system to load the new kernel.

🔧 Temporary Workarounds

Disable pktgen module

Linux

Unload the pktgen kernel module to prevent exploitation.

sudo rmmod pktgen

Blacklist pktgen module

Linux

Prevent pktgen from being loaded at boot.

echo 'blacklist pktgen' | sudo tee /etc/modprobe.d/blacklist-pktgen.conf
sudo update-initramfs -u

🧯 If You Can't Patch

Restrict access to pktgen by ensuring only trusted users have CAP_NET_ADMIN or root privileges.
Monitor system logs for kernel panics or UBSAN errors related to pktgen.

🔍 How to Verify

Check if Vulnerable:

Check if pktgen is loaded: 'lsmod | grep pktgen'. If loaded and kernel version is unpatched, system may be vulnerable.

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version includes fix commits: 'uname -r' and cross-reference with distribution kernel changelogs.

📡 Detection & Monitoring

Log Indicators:

Kernel logs (dmesg) showing 'UBSAN: array-index-out-of-bounds' or 'pktgen' errors, system crashes, or kernel panics.

Network Indicators:

Unusual packet generation activity if pktgen is exploited, but this is less likely.

SIEM Query:

Example: 'source="kernel" AND "pktgen" AND ("out-of-bounds" OR "UBSAN")'

📊 Metadata

CVE ID: CVE-2025-21680

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-129

Published: January 31, 2025

Last Updated: November 3, 2025

🔗 References

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🔗 Related Vulnerabilities

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