1. Ubuntu Security Notices
  2. USN-7939-1

USN-7939-1: Linux kernel (Azure) vulnerabilities

Publication date

16 December 2025

Overview

Several security issues were fixed in the Linux kernel.

Releases

Packages

Details

Jean-Claude Graf, Sandro Rüegge, Ali Hajiabadi, and Kaveh Razavi discovered
that the Linux kernel contained insufficient branch predictor isolation
between a guest and a userspace hypervisor for certain processors. This
flaw is known as VMSCAPE. An attacker in a guest VM could possibly use this
to expose sensitive information from the host OS. (CVE-2025-40300)

Several security issues were discovered in the Linux kernel.
An attacker could possibly use these to compromise the system.
This update corrects flaws in the following subsystems:

  • Cryptographic API;
  • ACPI drivers;
  • HSI subsystem;
  • I3C subsystem;
  • InfiniBand drivers;
  • Media drivers;
  • Network drivers;
  • Pin controllers subsystem;
  • AFS file system;
  • F2FS file system;
  • SMB network file system;
  • Padata parallel execution mechanism;
  • Timer...

Jean-Claude Graf, Sandro Rüegge, Ali Hajiabadi, and Kaveh Razavi discovered
that the Linux kernel contained insufficient branch predictor isolation
between a guest and a userspace hypervisor for certain processors. This
flaw is known as VMSCAPE. An attacker in a guest VM could possibly use this
to expose sensitive information from the host OS. (CVE-2025-40300)

Several security issues were discovered in the Linux kernel.
An attacker could possibly use these to compromise the system.
This update corrects flaws in the following subsystems:

  • Cryptographic API;
  • ACPI drivers;
  • HSI subsystem;
  • I3C subsystem;
  • InfiniBand drivers;
  • Media drivers;
  • Network drivers;
  • Pin controllers subsystem;
  • AFS file system;
  • F2FS file system;
  • SMB network file system;
  • Padata parallel execution mechanism;
  • Timer subsystem;
  • Tracing infrastructure;
  • Memory management;
  • Appletalk network protocol;
  • Networking core;
  • Netfilter

Update instructions

After a standard system update you need to reboot your computer to make all the necessary changes.

Learn more about how to get the fixes.

ATTENTION: Due to an unavoidable ABI change the kernel updates have been given a new version number, which requires you to recompile and reinstall all third party kernel modules you might have installed. Unless you manually uninstalled the standard kernel metapackages (e.g. linux-generic, linux-generic-lts-RELEASE, linux-virtual, linux-powerpc), a standard system upgrade will automatically perform this as well.

The problem can be corrected by updating your system to the following package versions:

Ubuntu Release Package Version
20.04 LTS focal linux-image-5.4.0-1156-azure –  5.4.0-1156.163  
linux-image-azure-5.4 –  5.4.0.1156.150  
linux-image-azure-lts-20.04 –  5.4.0.1156.150  
18.04 LTS bionic linux-image-5.4.0-1156-azure –  5.4.0-1156.163~18.04.1  
linux-image-azure –  5.4.0.1156.163~18.04.1  
linux-image-azure-5.4 –  5.4.0.1156.163~18.04.1  

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References

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