Testing for Web Services
4.8 Web Services Testing
"By 2005 Web services shall have reopened over 70% of the attack paths against internet-connected systems, which were closed by network firewalls in the 1990's" -Gartner Oct 2002
SOA (Service Orientated Architecture)/Web services applications are up-and-coming systems which are enabling businesses to interoperate and are growing at an unprecedented rate. Webservice "clients" are generally not user web front-ends but other backend servers. Webservices are exposed to the net like any other service but can be used on HTTP, FTP, SMTP, MQ among other transport protocols.
The vulnerabilities in web services are similar to other vulnerabilities such as SQL injection, information disclosure ad leakage etc but web services also have unique XML/parser related vulnerabilities which are discussed here also.
OWASP Testing Guide v2