What are some common XML security risks and how do you mitigate them?

1 XML Injection

XML injection is a type of attack where an attacker inserts malicious XML code into an XML document or message that is processed by your application. This can result in unauthorized access, data manipulation, or code execution. For example, an attacker could inject a fake element or attribute that changes the logic or output of your XML parser or validator. To prevent XML injection, you should always validate and sanitize your XML input using schema definitions, XML parsers, and XML filters that conform to web standards such as XML Schema, XML Signature, and XML Encryption. You should also avoid using dynamic or external entities that can introduce external dependencies or references.

2 XML External Entity (XXE)

XML external entity, or XXE, is a type of attack where an attacker exploits a feature of XML that allows the inclusion of external resources or entities in an XML document. This can result in information disclosure, denial of service, or remote code execution. For example, an attacker could use an XXE to access sensitive files, execute system commands, or trigger network requests from your server. To prevent XXE, you should disable or restrict the use of external entities in your XML parser or validator. You should also use web standards such as XML Schema and XML Signature to define and verify your XML documents and messages.

3 XML Denial of Service (XDoS)

XML denial of service, or XDoS, is a type of attack where an attacker sends large or complex XML documents or messages to your application that consume excessive resources or cause errors. This can result in performance degradation, service interruption, or system crash. For example, an attacker could use an XDoS to overload your CPU, memory, disk, or network bandwidth with recursive or nested entities, oversized or malformed elements, or multiple namespaces. To prevent XDoS, you should limit the size and complexity of your XML input using schema definitions, XML parsers, and XML filters. You should also implement rate limiting, caching, and load balancing techniques to handle high volumes of XML traffic.

4 XML Encryption and Signature Bypass

XML encryption and signature bypass is a type of attack where an attacker modifies or removes the encryption or signature elements of an XML document or message that are supposed to protect the data or identity of the sender or receiver. This can result in data tampering, impersonation, or repudiation. For example, an attacker could use an encryption or signature bypass to alter the content or destination of an XML message, forge the identity or credentials of an XML sender or receiver, or deny the authenticity or integrity of an XML transaction. To prevent encryption and signature bypass, you should use web standards such as XML Encryption and XML Signature to encrypt and sign your XML documents and messages. You should also use secure algorithms, keys, and certificates to ensure the confidentiality and validity of your encryption and signature processes.

5 XML Schema Poisoning

XML schema poisoning is a type of attack where an attacker modifies or replaces the schema definition of an XML document or message that is used by your application to validate and process the XML data. This can result in data corruption, logic errors, or code injection. For example, an attacker could use a schema poisoning to change the data type, format, or value of an XML element or attribute, introduce malicious elements or attributes, or execute arbitrary code through schema extensions or transformations. To prevent schema poisoning, you should always use trusted and verified sources for your schema definitions, such as web standards bodies or reputable organizations. You should also use web standards such as XML Schema and XML Signature to define and verify your schema definitions.