Security Update: qemu-kvm Vulnerability - VNC WebSocket Handshake Use-After-Free
Summary
ALSA-2026:1831: Moderate: qemu-kvm security update. Affects qemu-guest-agent versions < 18:10.0.0-14.el10_1.5.alma.1. Fixed in 18:10.0.0-14.el10_1.5.alma.1. How to fix ↓
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Background
Kernel-based Virtual Machine (KVM) is a full virtualization solution for Linux that allows users to run multiple virtual machines on a single physical host. The qemu-kvm package provides the user-space component necessary for managing these virtual machines. This package is essential for users who require virtualization capabilities on their AlmaLinux systems. However, a recent vulnerability has been identified that affects the qemu-kvm package, specifically related to the VNC WebSocket handshake process.
Vulnerability Detail
The vulnerability identified as CVE-2025-11234 is a use-after-free issue that occurs during the VNC WebSocket handshake. This flaw can potentially allow an attacker to execute arbitrary code or crash the virtual machine, leading to a denial of service. The vulnerability arises from improper memory management, where memory that has already been freed is accessed again, which can be exploited by malicious actors to gain unauthorized access or control over the affected system.
How To Fix
Minimum fixed version
18:10.0.0-14.el10_1.5.alma.1
This is the first release that contains the fix.
sudo dnf update qemu-guest-agentTip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary measure, users can disable VNC access to their virtual machines until the package is updated. This can be done by modifying the VM configuration to remove or disable the VNC display option.
Conclusion
The qemu-kvm vulnerability (CVE-2025-11234) poses a significant risk to users relying on KVM for virtualization. It is essential to update to the patched version of the package to mitigate potential threats. Users are encouraged to monitor their systems for vulnerabilities using tools like Vulert, which provides real-time alerts without requiring extensive setup.
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FAQ
CVE-2025-11234 is a vulnerability affecting the qemu-kvm package that involves a use-after-free issue during the VNC WebSocket handshake process.
You can use the Vulert platform to check if your application is affected by this vulnerability. Simply upload your manifest file like package-lock.json to monitor for vulnerabilities.
If exploited, this vulnerability could allow attackers to execute arbitrary code or crash the virtual machine, leading to potential data loss or service disruption.
Yes, a patch is available. Users should update their qemu-kvm package to version 18:10.0.0-14.el10_1.5.alma.1 or later.
If immediate updates are not possible, consider disabling VNC access to your virtual machines as a temporary workaround until the patch can be applied.
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