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.
Likelihood Of Attack
The table(s) below shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
Relevant to the view "Mechanisms of Attack" (CAPEC-1000)
Standard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.
The first step is exploratory meaning the attacker scans for WSDL documents. The WDSL document written in XML is like a handbook on how to communicate with the web services provided by the target host. It provides an open view of the application (function details, purpose, functional break down, entry points, message types, etc.). This is very useful information for the attacker.
The second step that an attacker would undertake is to analyze the WSDL files and try to find potential weaknesses by sending messages matching the pattern described in the WSDL file. The attacker could run through all of the operations with different message request patterns until a breach is identified.
Once an attacker finds a potential weakness, they can craft malicious content to be sent to the system. For instance the attacker may try to submit special characters and observe how the system reacts to an invalid request. The message sent by the attacker may not be XML validated and cause unexpected behavior.
A client program connecting to a web service can read the WSDL to determine what functions are available on the server.
The target host exposes vulnerable functions within its WSDL interface.
This attack can be as simple as reading WSDL and starting sending invalid request.
This attack can be used to perform more sophisticated attacks (SQL injection, etc.)
The table below specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
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.
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.
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Page Last Updated or Reviewed:
July 31, 2018
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