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 roots crontab file allows privilege escalation.
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Passenger | Phusion | 3.0.0 (including) | 5.3.2 (excluding) |
| Passenger | Ubuntu | artful | * |
| Passenger | Ubuntu | bionic | * |
| Passenger | Ubuntu | cosmic | * |
| Passenger | Ubuntu | disco | * |
| Passenger | Ubuntu | esm-apps/bionic | * |
| Passenger | Ubuntu | esm-apps/xenial | * |
| Passenger | Ubuntu | upstream | * |
| Passenger | Ubuntu | xenial | * |
| Ruby-passenger | Ubuntu | trusty | * |
A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:
A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.