local root compromise in hylafax

The HylaFax program hfaxd(8c) implements the server part of the HylaFax package. It is started either by inetd(8) or runs in standalone mode. hfaxd(8c) offers three different protocols to process fax jobs. When hfaxd(8c) tries to change to it’s queue directory and fails, it prints an error message via syslog by directly passing user supplied data as format string. As long as hfaxd(8c) is installed setuid root, this behavior could be exploited to gain root access locally.