Fourteen-Year-Old Linux Kernel Bug Lets Unprivileged Users Gain Root and Break Out of Docker

A flaw embedded in the Linux kernel’s AF_ALG cryptographic interface for more than a decade can be weaponized by a local attacker with no special privileges to obtain full system control and escape Docker containers, security researchers disclosed this week.

The vulnerability stems from a race condition that occurs when multiple processes write to the same AF_ALG socket simultaneously. By carefully timing these writes, an attacker can corrupt kernel memory, trigger an escalation path and ultimately execute code with root privileges. Because Docker containers share the host kernel, the same technique also permits a process confined to a container to break out and gain access to the underlying host.

The issue was originally reported by the independent security group GBHackers, who traced its origins back to code added to the kernel in 2009. Although the bug has lingered unnoticed for 14 years, it only became exploitable after recent changes to how the AF_ALG interface handles concurrent socket operations. The problem is cataloged under a CVE identifier, and the Linux kernel maintainers have classified it as a high‑severity vulnerability.

Linux powers a vast majority of servers, cloud platforms, and embedded devices, and Docker remains a cornerstone of modern application deployment. An exploit that bridges the container‑host boundary is particularly concerning for organizations that rely on container isolation as a primary security control. If left unpatched, the flaw could be used to compromise multi‑tenant environments, steal data, or install persistent backdoors.

Kernel maintainers responded quickly, issuing a patch that adds stricter synchronization checks to the AF_ALG socket implementation and eliminates the race condition. Distributions that ship updated kernels, including major Linux vendors such as Ubuntu, Debian, Red Hat, and SUSE, are expected to release security updates within the next few days. Administrators are urged to apply these updates promptly and to review any containers that expose AF_ALG‑related functionality.

Security experts note that the discovery highlights the challenges of maintaining legacy code in a rapidly evolving ecosystem. While the kernel’s open‑source model allows many eyes to scrutinize the code, subtle bugs can persist for years, especially in less‑frequently used subsystems. The incident serves as a reminder for organizations to adopt a defense‑in‑depth strategy, keep systems patched, and monitor container workloads for anomalous behavior.