Overview

CVE: CVE-2026-31431
Severity: Critical
Affected Systems: CaraOne servers running Ubuntu 22.04 with the linux-hwe-6.8 kernel
Coordinated with: Obvious Future development team

CVE-2026-31431 is a critical vulnerability in the Linux kernel's algif_aead module — part of the AF_ALG (Authenticated Encryption with Associated Data) crypto interface. On Ubuntu 22.04 systems running the linux-hwe-6.8 Hardware Enablement kernel, this vulnerability was flagged as critical and requires immediate mitigation on all affected CaraOne servers.

Following internal review, the Obvious Future development team confirmed that CaraOne does not depend on algif_aead functionality at runtime. The agreed mitigation path is to blacklist and unload the algif_aead kernel module across all affected CaraOne servers.

Affected Systems

  • Ubuntu 22.04 LTS (Jammy Jellyfish)
  • Kernel package: linux-hwe-6.8 (Hardware Enablement stack)
  • All CaraOne server nodes running the above configuration

Mitigation Steps

Run the following commands on each affected CaraOne server:

Step 1 — Blacklist the module (prevents auto-loading on boot)

echo "blacklist algif_aead" | sudo tee /etc/modprobe.d/blacklist-algif_aead.conf
sudo update-initramfs -u

Step 2 — Unload the module from the running kernel

sudo modprobe -r algif_aead

Step 3 — Verify the module is no longer loaded

lsmod | grep algif_aead

If the command returns no output, the module has been successfully unloaded.

Verification

  1. The module is not loaded (lsmod | grep algif_aead returns empty).
  2. The blacklist file exists at /etc/modprobe.d/blacklist-algif_aead.conf.
  3. The initramfs has been updated without errors.
  4. CaraOne services start and operate normally after the change.

Rollback

If any CaraOne functionality depends on algif_aead after the mitigation, roll back as follows:

sudo rm /etc/modprobe.d/blacklist-algif_aead.conf
sudo update-initramfs -u
sudo modprobe algif_aead

Notify the Obvious Future development team immediately if a rollback is required so an alternative mitigation path can be assessed.

Long-Term Resolution

This blacklist mitigation is a temporary measure pending a kernel patch for CVE-2026-31431. Monitor Ubuntu Security Notices (USN) for a patched linux-hwe-6.8 package. Once available and tested, apply via the standard CaraOne server patching process:

sudo apt update
sudo apt upgrade linux-hwe-6.8
sudo reboot

After rebooting to the patched kernel, remove the blacklist entry:

sudo rm /etc/modprobe.d/blacklist-algif_aead.conf
sudo update-initramfs -u

References

  • Ubuntu Security Notices: https://ubuntu.com/security/notices
  • NVD CVE entry: CVE-2026-31431
  • Coordinated with: Obvious Future development team (internal communication)