The issue is related to the incorrect use of the FD SET macro, which can trigger a stack-based buffer overflow when an application has a large number of open file descriptors. This can cause a denial of service, resulting in an application crash, and potentially allow for the execution of arbitrary code. The vulnerability is also related to the implementation of the select() and FD SET() functions in the nss-pam-ldapd package, which can lead to a file descriptor overflow.