Missing XML Validation
Draft Base
Structure: Simple
Description
The product accepts XML from an untrusted source but does not validate the XML against the proper schema.
Most successful attacks begin with a violation of the programmer's assumptions. By accepting an XML document without validating it against a DTD or XML schema, the programmer leaves a door open for attackers to provide unexpected, unreasonable, or malicious input.
Common Consequences 1
Scope: Integrity
Impact: Unexpected State
Detection Methods 1
Automated Static AnalysisHigh
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)Potential Mitigations 1
Phase: Architecture and Design
Strategy: Input Validation
Always validate XML input against a known XML Schema or DTD.
It is not possible for an XML parser to validate all aspects of a document's content because a parser cannot understand the complete semantics of the data. However, a parser can do a complete and thorough job of checking the document's structure and therefore guarantee to the code that processes the document that the content is well-formed.
Demonstrative Examples 2
The following code loads and parses an XML file.
Code Example:
Bad
Java
// Read DOM* try { ``` ... DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); factory.setValidating( false ); .... c_dom = factory.newDocumentBuilder().parse( xmlFile ); } catch(Exception ex) { ... }
The XML file is loaded without validating it against a known XML Schema or DTD.
The following code creates a DocumentBuilder object to be used in building an XML document.
Code Example:
Bad
Java
javaThe DocumentBuilder object does not validate an XML document against a schema, making it possible to create an invalid XML document.
References 1
Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors
Katrina Tsipenyuk, Brian Chess, and Gary McGraw
NIST Workshop on Software Security Assurance Tools Techniques and Metrics • NIST
07-11-2005
ID: REF-6
Applicable Platforms
Languages:
Not Language-Specific : Undetermined
Modes of Introduction
Implementation
Related Attack Patterns
Related Weaknesses
Taxonomy Mapping
- 7 Pernicious Kingdoms
- Software Fault Patterns