An issue was discovered in switchGroup() in agent/ExecHelper/ExecHelperMain.cpp in Phusion Passenger before 5.3.2. The set of groups (gidset) is not set correctly, leaving it up to randomness (i.e., uninitialized memory) which supplementary groups are actually being set while lowering privileges.

A race condition in the nginx module in Phusion Passenger 3.x through 5.x before 5.3.2 allows local escalation of privileges when a non-standard passenger_instance_registry_dir with insufficiently strict permissions is configured. Replacing a file with a symlink after the file was created, but before it was chowned, leads to the target of the link being chowned via the path. Targeting sensitive files such as root's crontab file allows privilege escalation.

An Incorrect Access Control vulnerability in SpawningKit in Phusion Passenger 5.3.x before 5.3.2 allows a Passenger-managed malicious application, upon spawning a child process, to report an arbitrary different PID back to Passenger's process manager. If the malicious application then generates an error, it would cause Passenger's process manager to kill said reported arbitrary PID.

An Insecure Permissions vulnerability in SpawningKit in Phusion Passenger 5.3.x before 5.3.2 causes information disclosure in the following situation: given a Passenger-spawned application process that reports that it listens on a certain Unix domain socket, if any of the parent directories of said socket are writable by a normal user that is not the application's user, then that non-application user can swap that directory with something else, resulting in traffic being redirected to a non-application user's process through an alternative Unix domain socket.

During the spawning of a malicious Passenger-managed application, SpawningKit in Phusion Passenger 5.3.x before 5.3.2 allows such applications to replace key files or directories in the spawning communication directory with symlinks. This then could result in arbitrary reads and writes, which in turn can result in information disclosure and privilege escalation.