An issue was discovered in atftpd in atftp 0.7.1. It does not lock the thread_list_mutex mutex before assigning the current thread data structure. As a result the daemon is vulnerable to a denial of service attack due to a NULL pointer dereference. If thread_data is NULL when assigned to current and modified by another thread before a certain tftpd_list.c check there is a crash when dereferencing current->next.