CVE-2024-26999 – A race condition in the Linux kernel's pmac

Q: What is the severity of CVE-2024-26999?

CVE-2024-26999 has a CVSS score of 5.5 (MEDIUM). A race condition in the Linux kernel's pmac_zilog serial driver can cause a kernel panic or system crash when used as a serial console. This affects Linux systems using PowerPC architecture with the vulnerable driver loaded, particularly older Apple Power Macintosh hardware or QEMU emulation.

📋 TL;DR

A race condition in the Linux kernel's pmac_zilog serial driver can cause a kernel panic or system crash when used as a serial console. This affects Linux systems using PowerPC architecture with the vulnerable driver loaded, particularly older Apple Power Macintosh hardware or QEMU emulation.

💻 Affected Systems

Products:

Linux kernel

Versions: Kernel versions before the fix commits (specific versions vary by distribution)

Operating Systems: Linux distributions running on PowerPC architecture

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when pmac_zilog driver is loaded and used as serial console, primarily affects PowerPC systems like older Apple Power Macintosh hardware.

📦 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...

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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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⚠️ Risk & Real-World Impact

🔴

Worst Case

System crash or kernel panic leading to denial of service, potentially requiring physical access to reboot affected systems.

🟠

Likely Case

System instability or crash when the serial console receives high interrupt rates, causing denial of service.

🟢

If Mitigated

Minimal impact if system doesn't use pmac_zilog driver or serial console functionality.

🌐 Internet-Facing: LOW - Requires local access or specific hardware configuration to trigger.

🏢 Internal Only: LOW - Only affects specific PowerPC systems with serial console usage.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: NO

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires local access and ability to generate high interrupt rates on serial port, or specific QEMU configurations.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions containing commits 1be3226445362bfbf461c92a5bcdb1723f2e4907 or later

Vendor Advisory: https://git.kernel.org/stable/c/1be3226445362bfbf461c92a5bcdb1723f2e4907

Restart Required: Yes

Instructions:

1. Update Linux kernel to version containing the fix commit. 2. For distributions: Use package manager (apt/yum/dnf) to update kernel package. 3. Reboot system to load new kernel.

🔧 Temporary Workarounds

Disable pmac_zilog driver

linux

Prevent loading of vulnerable driver if not needed

echo 'blacklist pmac_zilog' >> /etc/modprobe.d/blacklist.conf
update-initramfs -u

Avoid serial console usage

linux

Configure system to not use serial console if possible

Remove 'console=ttyPZ0' or similar from kernel command line in /boot/grub/grub.cfg or /etc/default/grub

🧯 If You Can't Patch

Ensure system does not use serial console functionality
Monitor system logs for 'pmz: rx irq flood' messages and investigate any serial port issues

🔍 How to Verify

Check if Vulnerable:

Check if pmac_zilog module is loaded: lsmod | grep pmac_zilog AND check kernel version against patched versions

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version includes fix commit: grep -q '1be3226445362bfbf461c92a5bcdb1723f2e4907' /proc/version_signature (if available) OR check distribution kernel changelog

📡 Detection & Monitoring

Log Indicators:

Kernel messages containing 'pmz: rx irq flood'
Kernel panic or BUG splat messages related to spinlock recursion

Network Indicators:

None - local vulnerability only

SIEM Query:

source="kernel" AND ("pmz: rx irq flood" OR "spinlock recursion" AND "pmz")

📊 Metadata

CVE ID: CVE-2024-26999

CVSS v3 Score: 5.5 (MEDIUM)

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

CWE: CWE-667

Published: May 1, 2024

Last Updated: November 4, 2025

🔗 References

https://git.kernel.org/stable/c/1be3226445362bfbf461c92a5bcdb1723f2e4907 Mailing List,Patch
https://git.kernel.org/stable/c/52aaf1ff14622a04148dbb9ccce6d9de5d534ea7 Mailing List,Patch
https://git.kernel.org/stable/c/69a02273e288011b521ee7c1f3ab2c23fda633ce Mailing List,Patch
https://git.kernel.org/stable/c/7a3bbe41efa55323b6ea3c35fa15941d4dbecdef Mailing List,Patch
https://git.kernel.org/stable/c/ab86cf6f8d24e63e9aca23da5108af1aa5483928 Mailing List,Patch
https://git.kernel.org/stable/c/bbaafbb4651fede8d3c3881601ecaa4f834f9d3f Mailing List,Patch
https://git.kernel.org/stable/c/ca09dfc3cfdf89e6af3ac24e1c6c0be5c575a729 Mailing List,Patch
https://git.kernel.org/stable/c/d679c816929d62af51c8e6d7fc0e165c9412d2f3 Mailing List,Patch
https://git.kernel.org/stable/c/1be3226445362bfbf461c92a5bcdb1723f2e4907 Mailing List,Patch
https://git.kernel.org/stable/c/52aaf1ff14622a04148dbb9ccce6d9de5d534ea7 Mailing List,Patch
https://git.kernel.org/stable/c/69a02273e288011b521ee7c1f3ab2c23fda633ce Mailing List,Patch
https://git.kernel.org/stable/c/7a3bbe41efa55323b6ea3c35fa15941d4dbecdef Mailing List,Patch
https://git.kernel.org/stable/c/ab86cf6f8d24e63e9aca23da5108af1aa5483928 Mailing List,Patch
https://git.kernel.org/stable/c/bbaafbb4651fede8d3c3881601ecaa4f834f9d3f Mailing List,Patch
https://git.kernel.org/stable/c/ca09dfc3cfdf89e6af3ac24e1c6c0be5c575a729 Mailing List,Patch
https://git.kernel.org/stable/c/d679c816929d62af51c8e6d7fc0e165c9412d2f3 Mailing List,Patch
https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html Mailing List
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/4EZ6PJW7VOZ224TD7N4JZNU6KV32ZJ53/
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/DAMSOZXJEPUOXW33WZYWCVAY7Z5S7OOY/
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/GCBZZEC7L7KTWWAS2NLJK6SO3IZIL4WW/

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