CISA Warns of Critical Linux Kernel CVE-2024-XXXX Zero-Day Exploited in Attacks

Key Takeaways

• The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has issued an urgent warning regarding a critical Linux kernel zero-day vulnerability, CVE-2026-31431, actively exploited in the wild.
• Dubbed “Copy Fail,” this high-severity flaw (CVSS 7.8) allows unprivileged local users to escalate privileges to root on affected systems.
• The vulnerability impacts a wide range of popular Linux distributions, including Ubuntu, Red Hat, Amazon Linux, SUSE, Debian, Fedora, and Arch Linux, specifically kernels built since 2017.
• Patches are available in Linux kernel versions 6.18.22, 6.19.12, and 7.0, with CISA mandating immediate remediation for federal agencies.

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has added a critical Linux kernel zero-day vulnerability to its Known Exploited Vulnerabilities (KEV) catalog, urging federal agencies and organizations globally to apply patches immediately or cease using affected systems. The flaw, designated CVE-2026-31431 and nicknamed “Copy Fail,” carries a CVSS score of 7.8, classifying it as a high-severity issue, and falls under the CWE-699 category for incorrect resource transfer.

This vulnerability resides within the algif_aead module of the Linux kernel’s AF_ALG cryptographic subsystem. Specifically, it is a logic error in the authentication cryptographic template that leads to improper memory handling during in-place operations. Its exploitability is particularly concerning, as an unprivileged local user can reliably escalate privileges to root using a mere 732-byte Python script.

A Decade in the Making

Although publicly disclosed on April 29, 2026, the roots of this vulnerability trace back nearly a decade. It originated from three distinct, individually innocuous changes introduced into the Linux kernel in 2011, 2015, and 2017. None of these modifications independently raised any security concerns at the time.

The flaw impacts virtually every major Linux distribution featuring kernels built since 2017. This extensive list includes Ubuntu 24.04 LTS, Amazon Linux 2023, Red Hat Enterprise Linux 10.1, SUSE 16, Debian, Fedora, and Arch Linux.

The attack chain leverages an interaction between the AF_ALG socket interface, the splice() system call, and inadequate error handling during a failed copy operation. This sequence allows an attacker to achieve a controlled 4-byte overwrite within the kernel page cache. The overwrite facilitates the corruption of setuid binaries and other sensitive kernel-managed data, all within kernel space, effectively bypassing traditional user-space protections.

Crucially, successful exploitation does not require root privileges inside containers, kernel modules, or network access. This makes “Copy Fail” an extremely potent post-exploitation tool, particularly dangerous in containerized environments such as Kubernetes clusters and Docker CI runners.

CISA officially added CVE-2026-31431 to its KEV catalog on May 1, 2026, imposing a mandatory remediation deadline of May 15, 2026, for all federal civilian agencies. Patches are now available in Linux kernel versions 6.18.22, 6.19.12, and 7.0. Organizations utilizing Red Hat Enterprise Linux can implement configuration-level mitigations while awaiting patch deployment.

CISA directs all organizations to apply vendor-issued mitigations without delay, adhere to BOD 22-01 guidance for cloud services, or discontinue the use of unpatched systems. Security teams are strongly advised to audit Linux kernel versions across all cloud workloads, container environments, and on-premises infrastructure immediately, given confirmed reports of active exploitation in the wild.

What You Should Do

• Immediately update Linux kernel versions to 6.18.22, 6.19.12, 7.0, or newer patched versions provided by your distribution vendor.
• For Red Hat Enterprise Linux users, apply configuration-level mitigations as advised by Red Hat while awaiting full patches.
• Conduct a comprehensive audit of all Linux-based systems, including cloud instances, containerized environments (Docker, Kubernetes), and on-premises infrastructure, to identify and prioritize affected systems.
• Follow CISA’s BOD 22-01 guidance for cloud services and ensure compliance with all federal agency directives.
• If immediate patching is not feasible, consider isolating or discontinuing the use of vulnerable systems until they can be secured.

Disclaimer: HackersRadar reports on cybersecurity threats and incidents for informational and awareness purposes only. We do not engage in hacking activities, data exfiltration, or the hosting or distribution of stolen or leaked information. All content is based on publicly available sources.