What is CVE-2026-31431 (Copy Fail)?
On April 29, 2026, a critical security vulnerability in the Linux kernel was publicly disclosed under the identifier CVE-2026-31431, commonly referred to as Copy Fail.
This vulnerability is classified as a Local Privilege Escalation (LPE) issue, meaning an attacker with local access to a system can exploit it to gain root-level privileges, the highest level of control in Linux systems.
The flaw exists in a kernel module called algif_aead, which is responsible for providing hardware-accelerated cryptographic operations.
Severity and Risk Level
The vulnerability has been assigned a CVSS 3.1 score of 7.8, categorizing it as HIGH severity.
This level of severity indicates a significant risk, especially for multi-user systems and production environments.
Impact Analysis
Systems Without Containers
On systems that do not use containerized workloads, any local user can exploit this vulnerability to escalate privileges to root. A working exploit has already been publicly released for this scenario.
Containerized Environments
In environments using containers (such as Docker or Kubernetes), the vulnerability could potentially allow container escape, enabling attackers to break out of isolated environments and access the host system. While a public proof-of-concept is not yet available, the risk remains high.
Affected Systems
The vulnerability affects most Ubuntu releases prior to Resolute 26.04, including:
Ubuntu 18.04 (Bionic)
Ubuntu 20.04 (Focal)
Ubuntu 22.04 (Jammy)
Ubuntu 24.04 (Noble)
Ubuntu 25.10 (Questing)
The issue is fixed in Ubuntu 26.04 (Resolute).
How to Check if Your System is Vulnerable
Check your current kernel version:
uname -r
List installed kernel packages:
dpkg -l 'linux-image*' | grep ^ii
Check the installed version of kmod:
dpkg -l kmod
Compare your versions with the official patched versions to determine if your system is affected.
How to Fix the Vulnerability
Recommended Solution (Full System Update)
sudo apt update && sudo apt upgrade
This ensures your system receives the latest kernel patches and security fixes.
Partial Fix (Update kmod Only)
If a full upgrade is not possible:
sudo apt update && sudo apt install --only-upgrade kmod
Temporary Mitigation (Without Reboot)
You can disable the vulnerable kernel module:
sudo rmmod algif_aead
Verify if it is still loaded:
grep '^algif_aead' /proc/modules
Important Notes
Disabling the module may impact performance, as cryptographic operations will fall back to software-based implementations.
Some running applications may require a restart to function properly.
In many cases, a system reboot is recommended to fully apply the mitigation.
Manual Mitigation (Alternative Method)
If updating kmod is not possible, manually block the module:
echo "install algif_aead /bin/false" | sudo tee /etc/modprobe.d/manual-disable-algif_aead.conf
❗ Should You Be Concerned?
Yes — especially if:
Your system has multiple users
You run containerized workloads
You manage production servers
Conclusion
The CVE-2026-31431 (Copy Fail) vulnerability poses a serious security threat to Linux systems by enabling privilege escalation.
The best course of action is to update your system immediately. If that’s not feasible, apply temporary mitigations to reduce risk until a full patch can be deployed.