runc Container Escape Flaws Expose Hosts to Root Compromise

Researchers disclosed three new runc vulnerabilities — CVE-2025-31133, CVE-2025-52565, and CVE-2025-52881 — that can let attackers break container isolation and gain root access on the host systems running Docker, Kubernetes, and other platforms built on runc. The flaws abuse race conditions, mount manipulation, and redirected writes into procfs, including paths such as /proc/sys/kernel/core_pattern and /proc/sysrq-trigger, to turn container access into host-level impact. Sysdig reported that exploitation requires the ability to launch containers with custom mount configurations, making malicious or untrusted container images and Dockerfiles a likely delivery path, and said no active exploitation had been observed at disclosure.

The new issues echo the earlier CVE-2019-5736 runC escape, which allowed container root users to overwrite the host runC binary via /proc/self/exe and /proc/[pid]/exe handling and then execute code as root on the host. That earlier flaw affected Docker by default and also impacted LXC in some configurations, leading maintainers to harden runC by re-executing from a sealed in-memory copy created with memfd_create(). For the newly disclosed bugs, fixed releases are runc 1.2.8, 1.3.3, and 1.4.0-rc.3 or later, and defenders were advised to monitor for suspicious symlink creation and other attempts to target sensitive procfs entries from inside containers.