Linux Kernel cgroups v1 release_agent improper-authentication container escape added to CISA KEV — patch due 2026-06-05
CISA added the four-year-old cgroups v1 release_agent privilege-escalation bug to KEV today with a 2026-06-05 deadline. The vulnerable shape is a container that holds CAP_SYS_ADMIN and can write to a cgroup v1 release_agent file in an unprivileged user namespace — the kernel runs the configured agent as root on the host when the cgroup empties. This is the canonical container-escape primitive that has been in offensive tradecraft since 2022; the KEV add likely reflects a fresh campaign chaining it after an initial RCE. If you still run cgroup v1 hosts (older RHEL, custom kernels), audit for containers running with CAP_SYS_ADMIN and migrate to cgroup v2 where the release_agent surface no longer exists.