4.0

36
Web Application Penetration Testing
901/tcp open http Samba SWAT administration server
1241/tcp open ssl Nessus security scanner
3690/tcp open unknown
8000/tcp open http-alt?
8080/tcp open http Apache Tomcat/Coyote JSP engine 1.1
From this example, one see that:
• There is an Apache http server running on port 80.
• It looks like there is an https server on port 443 (but this needs to
be confirmed, for example, by visiting https:/192.168.1.100 with a
browser).
• On port 901 there is a Samba SWAT web interface.
• The service on port 1241 is not https, but is the SSL-wrapped Nessus
daemon.
• Port 3690 features an unspecified service (nmap gives back its
fingerprint - here omitted for clarity - together with instructions
to submit it for incorporation in the nmap fingerprint database,
provided you know which service it represents).
• Another unspecified service on port 8000; this might possibly be
http, since it is not uncommon to find http servers on this port. Let’s
examine this issue:
Interesting ports on 192.168.1.100:
(The 65527 ports scanned but not shown below are in state:
closed)
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 3.5p1 (protocol 1.99)
80/tcp open http Apache httpd 2.0.40 ((Red Hat Linux))
443/tcp open ssl OpenSSL
This confirms that in fact it is an HTTP server. Alternatively, testers
could have visited the URL with a web browser; or used the GET or
HEAD Perl commands, which mimic HTTP interactions such as the
one given above (however HEAD requests may not be honored by all
servers).
• Apache Tomcat running on port 8080.
The same task may be performed by vulnerability scanners, but first
check that the scanner of choice is able to identify http[s] services
running on non-standard ports. For example, Nessus [3] is capable of
identifying them on arbitrary ports (provided it is instructed to scan all
the ports), and will provide, with respect to nmap, a number of tests
on known web server vulnerabilities, as well as on the SSL configuration
of https services. As hinted before, Nessus is also able to spot
popular applications or web interfaces which could otherwise go unnoticed
(for example, a Tomcat administrative interface).
Approaches to address issue 3 - virtual hosts
There are a number of techniques which may be used to identify DNS
names associated to a given IP address x.y.z.t.
DNS zone transfers
This technique has limited use nowadays, given the fact that zone
transfers are largely not honored by DNS servers. However, it may
be worth a try. First of all, testers must determine the name servers
serving x.y.z.t. If a symbolic name is known for x.y.z.t (let it be www.
example.com), its name servers can be determined by means of tools
such as nslookup, host, or dig, by requesting DNS NS records.
If no symbolic names are known for x.y.z.t, but the target definition
contains at least a symbolic name, testers may try to apply the same
process and query the name server of that name (hoping that x.y.z.t
will be served as well by that name server). For example, if the target
consists of the IP address x.y.z.t and the name mail.example.com, determine
the name servers for domain example.com.
The following example shows how to identify the name servers for
www.owasp.org by using the host command:
$ host -t ns www.owasp.org
www.owasp.org is an alias for owasp.org.
owasp.org name server ns1.secure.net.
owasp.org name server ns2.secure.net.
A zone transfer may now be requested to the name servers for domain
example.com. If the tester is lucky, they will get back a list of the
DNS entries for this domain. This will include the obvious www.example.com
and the not-so-obvious helpdesk.example.com and webmail.
example.com (and possibly others). Check all names returned by the
zone transfer and consider all of those which are related to the target
being evaluated.
Trying to request a zone transfer for owasp.org from one of its name
servers:
$ host -l www.owasp.org ns1.secure.net
Using domain server:
Name: ns1.secure.net
Address: 192.220.124.10#53
Aliases:
Host www.owasp.org not found: 5(REFUSED)
; Transfer failed.
DNS inverse queries
This process is similar to the previous one, but relies on inverse (PTR)
DNS records. Rather than requesting a zone transfer, try setting the
record type to PTR and issue a query on the given IP address. If the
testers are lucky, they may get back a DNS name entry. This technique
relies on the existence of IP-to-symbolic name maps, which is not
guaranteed.
Web-based DNS searches
This kind of search is akin to DNS zone transfer, but relies on webbased
services that enable name-based searches on DNS. One
such service is the Netcraft Search DNS service, available at http:/
searchdns.netcraft.com/?host. The tester may query for a list of
names belonging to your domain of choice, such as example.com.
Then they will check whether the names they obtained are pertinent
to the target they are examining.