Common Attack Pattern Enumeration and Classification
A Community Resource for Identifying and Understanding Attacks
This attack targets the WSDL interface made available by a web service. The attacker may scan the WSDL interface to reveal sensitive information about invocation patterns, underlying technology implementations and associated vulnerabilities. This type of probing is carried out to perform more serious attacks (e.g. parameter tampering, malicious content injection, command injection, etc.). WSDL files provide detailed information about the services ports and bindings available to consumers. For instance, the attacker can submit special characters or malicious content to the Web service and can cause a denial of service condition or illegal access to database records. In addition, the attacker may try to guess other private methods by using the information provided in the WSDL files.
A WSDL interface may expose a function vulnerable to SQL Injection.
The Web Services Description Language (WSDL) allows a web service to advertise its capabilities by describing operations and parameters needed to access the service. As discussed in step 5 of this series, WSDL is often generated automatically, using utilities such as Java2WSDL, which takes a class or interface and builds a WSDL file in which interface methods are exposed as web services.
Because WSDL generation often is automated, enterprising adversaries can use WSDL to gain insight into the both public and private services. For example, an organization converting legacy application functionality to a web services framework may inadvertently pass interfaces not intended for public consumption to a WSDL generation tool. The result will be SOAP interfaces that give access to private methods.
Another, more subtle WSDL attack occurs when an enterprising attacker uses naming conventions to guess the names of unpublished methods that may be available on the server. For example, a service that offers a stock quote and trading service may publish query methods such as requestStockQuote in its WSDL. However, similar unpublished methods may be available on the server but not listed in the WSDL, such as executeStockQuote. A persistent adversary with time and a library of words and phrases can cycle thru common naming conventions (get, set, update, modify, and so on) to discover unpublished application programming interfaces that open doors into private data and functionality.
Source : "Seven Steps to XML Mastery, Step 7: Ensure XML Security", Frank Coyle. See reference section.
Skill or Knowledge Level: Low
This attack can be as simple as reading WSDL and starting sending invalid request.
Skill or Knowledge Level: Medium
This attack can be used to perform more sophisticated attacks (SQL injection, etc.)
An attacker can request the WSDL file from the target host by sending a SOAP message.
There are free Vulnerability testing tool, such as WSDigger to perform WSDL scanning - Foundstone's free Web services security tool performs WSDL scanning, SQL injection and XSS attacks on Web Services.
It is important to protect WSDL file or provide limited access to it.
Review the functions exposed by the WSDL interface (especially if you have used a tool to generate it). Make sure that none of them is vulnerable to injection.
Ensure the WSDL does not expose functions and APIs that were not intended to be exposed.
Pay attention to the function naming convention (within the WSDL interface). Easy to guess function name may be an entry point for attack.
Validate the received messages against the WSDL Schema. Incomplete solution.
[R.95.1] [REF-3] "Common Weakness Enumeration (CWE)". CWE-20 - Input Validation. Draft. The MITRE Corporation. 2007. <http://cwe.mitre.org/data/definitions/20.html>.
[R.95.2] Walid Negm. "Anatomy of a Web Services Attack". ForumSystems. March 1, 2004. <http://www.forumsys.com/resources/resources/whitepapers/archive//Anatomy_of_Attack_wp.pdf>.
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