Top 10 Web services threats

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Securing XML

The most frequent techniques used to attack Web services:

1. Coercive parsing. This attack exploits the interfaces used to link legacy systems with Extensible Markup Language components in an existing infrastructure. It can overwhelm a system's processing capabilities or install malicious mobile code.

2. Parameter tampering. Parameters send client-specific information to the Web service so that a certain remote operation can be executed. Instructions on how to use parameters are described in a Web Services Description Language (WSDL) document, and someone could manipulate the parameter options to retrieve unauthorized information.

3. Recursive payload. XML can nest elements within a document to address complex relationships such as a purchase order that includes shipping and billing addresses and quantities. Attackers can attempt to break an XML parser by creating a file with massive amounts of data.

4. Oversized payload. Because XML is verbose in the way it marks up existing data and information, file size is always a consideration. Programmers can limit a document's size, but there are a number of reasons why it might be hundreds of megabytes or gigabytes. But large sizes also could mean an attacker has manipulated the parser to execute a denial-of-service attack.

5. Schema poisoning. XML schemas provide specific details about documents' grammar

and templates from which parsers interpret them. Because they describe necessary preprocessing instructions, they are vulnerable to tampering.

6. WSDL scanning. WSDL is a mechanism for Web services to dynamically describe the parameters used when connecting to commands that accept input from external sources. However, these files are often built automatically using utilities designed to expose and describe all information available in a command. An attacker might cycle through the command and string combinations to discover unintentionally related or unpublished application program interfaces.

7. Routing detour. The Web Services-Routing specification helps direct XML traffic through an environment by allowing a way station in an XML path to assign routing instructions to a document. The way stations can be compromised, allowing attackers to insert bogus instructions to reroute a confidential file. They can then strip out the malicious instructions before forwarding the document to its destination.

8. External entity attack. XML can build documents dynamically by pointing to a Uniform Resource Identifier where the actual data exists. However, an attacker can replace the data being retrieved with malicious data.

9. SQL injection. By executing multiple commands in an input file, attackers can create invalidated SQL commands.

10. Replay attack. In this attack, hackers issue repetitive Simple Object Access Protocol messages to overload a Web service.

Source: Spire Security LLC

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