Common Attack Pattern Enumeration and Classification
A Community Resource for Identifying and Understanding Attacks
An attacker utilizes crafted XML user-controllable input to probe, attack, and inject data into the XML database, using techniques similar to SQL injection. The user-controllable input can allow for unauthorized viewing of data, bypassing authentication or the front-end application for direct XML database access, and possibly altering database information.
Consider an application that uses an XML database to authenticate its users. The application retrieves the user name and password from a request and forms an XPath expression to query the database. An attacker can successfully bypass authentication and login without valid credentials through XPath Injection. This can be achieved by injecting the query to the XML database with XPath syntax that causes the authentication check to fail. Improper validation of user-controllable input and use of a non-parameterized XPath expression enable the attacker to inject an XPath expression that causes authentication bypass.
Skill or Knowledge Level: Low
An attacker must have knowledge of XML syntax and constructs in order to successfully leverage XML Injection
The attacker tries to inject characters that can cause an error, such as single-quote (') or equal sign (=), or content that may cause a malformed XML expression. If the injection of such content into the input causes an XPath error and the resulting error is displayed unfiltered, the attacker can begin to determine the nature of input validation and structure of XPath expressions used in queries.
Too many exceptions generated by the application as a result of malformed queries
Strong input validation - All user-controllable input must be validated and filtered for illegal characters as well as content that can be interpreted in the context of an XML data or a query.
Use of custom error pages - Attackers can glean information about the nature of queries from descriptive error messages. Input validation must be coupled with customized error pages that inform about an error without disclosing information about the database or application.
The impact of payload activation is that it is interpreted as part of the XPath expression used in the query, thus enabling an attacker to modify the expression used by the query.
Special characters in user-controllable input must be escaped before use by the application.
Custom error pages must be used to handle exceptions such that they do not reveal any information about the architecture of the application or the database.
[R.250.1] [REF-3] "Common Weakness Enumeration (CWE)". CWE-91 - XML Injection. Draft. The MITRE Corporation. 2007. <http://cwe.mitre.org/data/definitions/91.html>.
[R.250.2] [REF-3] "Common Weakness Enumeration (CWE)". CWE-20 - Input Validation. Draft. The MITRE Corporation. 2007. <http://cwe.mitre.org/data/definitions/20.html>.
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