polkit: unbounded stdin read in polkit-agent-helper-1 lets a local user exhaust system memory

Impact

The setuid polkit-agent-helper-1 binary reads input from stdin without a length bound, so a local user piping an arbitrarily long string into it can push the machine into an out-of-memory condition and take down whatever the OOM killer selects. There is no privilege escalation described, only denial of service. The exposure is limited to hosts where untrusted users hold a real shell: HPC login and head nodes, bastions, and shared submit hosts. A GPU compute node that only ever runs tenant containers, with no interactive host accounts, is not reachable this way unless polkit is present and callable from inside the container namespace.

Who can reach it

A local user with an unprivileged shell on the host. No network access and no existing privilege beyond a login account is required.

What to do

Update the polkit package once your distribution ships the fix. Red Hat is tracking it across RHEL 6 through 10 and OpenShift Container Platform 4 and the upstream project is freedesktop polkit, but the record names no fixed version, so pull it from the vendor page for your stream. No reboot and no service restart is needed, because the helper is spawned fresh on each authentication, so the new binary takes effect immediately. Where patching lags, per-user memory limits (cgroup limits or RLIMIT_AS via limits.conf) on shared login nodes contain the blast radius.

References