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Individual CAPEC Dictionary Definition (Release 1.1)
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XPath Injection | |||||||||||||||||||||||||||||
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| Attack Pattern ID | Pattern Abstraction: Detailed 83 | ||||||||||||||||||||||||||||
| Typical Severity | High | ||||||||||||||||||||||||||||
| Description | Summary An attacker can craft special user-controllable input consisting of XPath expressions to inject the XML database and bypass authentication or glean information that he normally would not be able to. XPath Injection enables an attacker to talk directly to the XML database, thus bypassing the application completely. XPath Injection results form the failure of an application to properly sanitize input used as part of dynamic XPath expressions used to query an XML database. In order to successfully inject XML and retrieve information from a database, an attacker: Attack Execution Flow
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| Attack Prerequisites | XPath queries used to retrieve information stored in XML documents User-controllable input not properly sanitized before being used as part of XPath queries | ||||||||||||||||||||||||||||
| Typical Likelihood of Exploit | High | ||||||||||||||||||||||||||||
| Methods of Attack |
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| Examples-Instances | Description 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. | ||||||||||||||||||||||||||||
| Attacker Skill or Knowledge Required | Low - XPath Injection shares the same basic premises with SQL Injection. An attacker must have knowledge of XPath synax and constructs in order to successfully leverage XPath Injection | ||||||||||||||||||||||||||||
| Resources Required | None | ||||||||||||||||||||||||||||
| Probing Techniques | The attacker tries to inject characters that can cause an XPath error, such as single-quote ('), or content that may cause a malformed XPath 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. | ||||||||||||||||||||||||||||
| Indicators-Warnings of Attack | Too many exceptions generated by the appplication as a result of malformed XPath queries | ||||||||||||||||||||||||||||
| Solutions and Mitigations | 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 XPath expression. Characters such as a single-quote(') or operators such as or (|), and (&) and such should be filtered if the application does not expect them in the context in which they appear. If such content cannot be filtered, it must at least be properly escaped to avoid them being interpreted as part of XPath expressions. Use of parameterized XPath queries - Parameterization causes the input to be restricted to certain domains, such as strings or integers, and any input outside such domains is considered invalid and the query fails. 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. | ||||||||||||||||||||||||||||
| Attack Motivation- |
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| Context Description | The primary cause of XPath Injection is use of improperly validated input. In the absence of such validation, it becomes possible to inject content that can be interpreted as part of XPath expressions used in querying the XML database. The second most important reason is use of XPath expressions created dynamically to query the database. Another factor, albeit a minor one, is the use of default error pages that reveal information about the structure of XPath queries. | ||||||||||||||||||||||||||||
| Injection Vector | User-controllable input used as part of dynamic XPath queries | ||||||||||||||||||||||||||||
| Payload | XPath expressions intended to defeat checks run by XPath queries | ||||||||||||||||||||||||||||
| Activation Zone | XML database | ||||||||||||||||||||||||||||
| Payload Activation Impact | 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. | ||||||||||||||||||||||||||||
| Related Weaknesses |
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| Relevant Security Requirements | Special characters in user-controllable input must be escaped before use by the application. Only use parameterized XPath expressions to query the XML database. 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. | ||||||||||||||||||||||||||||
| Related Security Principles |
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| Related Guidelines |
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| Purpose | Penetration Exploitation | ||||||||||||||||||||||||||||
| CIA Impact |
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| Technical Context |
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| References | CWE - XML Injection CWE - Input Validation CWE - Improper Error Handling | ||||||||||||||||||||||||||||
| Source |
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