Screen version 5.0.0 and older version 4 releases have a TOCTOU race potentially allowing to send SIGHUP, SIGCONT to privileged processes when installed setuid-root.
The product checks the state of a resource before using that resource, but the resource’s state can change between the check and the use in a way that invalidates the results of the check. This can cause the product to perform invalid actions when the resource is in an unexpected state.