setupBpmLogs follows symlink for bpm.log open and chown — container-to-host privilege escalation via /etc/shadow

setupBpmLogs follows symlink for bpm.log open and chown — container-to-host privilege escalation via /etc/shadow. A compromised process inside a bpm container can cause root to chown an arbitrary host file to vcap and append bpm JSON log lines to it. The chown alone lets the attacker take ownership of /etc/shadow and read every password hash on the host via the read-only /etc bind mount. This is a container-to-host confidentiality break affecting every bpm-managed job.

Affected versions: bpm-release, all versions prior to v1.4.30.