I. THE SYSTEM
Symantec Gateway Security (SGS) is an enterprise-class appliance with a
linux-based stateful inspection firewall and application proxy
capabilities (http/https, ftp, smtp, dns, and so on).
Using the default installation the system keeps listening on the WAN
interface for all its proxies. All the proxies use an authentication
system and everything seems ok. DNS until now can not use authentication
system
2. THE EXPLIT
could connect to the 53/tcp or 53/udp ports of the SGS and use it as a
dns server, for instance to make some "noisy" queries to primary dns
servers (zone transfers, and so on). This could be a problem if,for
instance, those types of queries are logged: in this case the source ip
will be the address of the SGS
3. THE SLUTIN
A solution could be, for instance, to create a filter (i.e. an iptables
rule) in the SGS to cutoff all the queries coming from outside, taking
into account some particular situation as, for instance, VPNs or DMZs on
the red interface