CWE-91: XML Injection (aka Blind XPath Injection) (Base)

Description: The product does not properly neutralize special elements that are used in XML, allowing attackers to modify the syntax, content, or commands of the XML before it is processed by an end system.

Extended Description: Within XML, special elements could include reserved words or characters such as <, >, , and &, which could then be used to add new data or modify XML syntax.



Applicable Platforms: ::LANGUAGE CLASS:Not Language-Specific:LANGUAGE PREVALENCE:Undetermined::

Modes of Introduction: ::PHASE:Implementation:NOTE:REALIZATION: This weakness is caused during implementation of an architectural security tactic.::



Common Consequences: ::SCOPE:Confidentiality:SCOPE:Integrity:SCOPE:Availability:IMPACT:Execute Unauthorized Code or Commands:IMPACT:Read Application Data:IMPACT:Modify Application Data::

Detection Methods: ::METHOD:Automated Static Analysis:DESCRIPTION: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.):EFFECTIVENESS:High::

Potential Mitigations: ::PHASE:Implementation:STRATEGY:Input Validation:DESCRIPTION:Assume all input is malicious. Use an accept known good input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, boat may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as red or blue. Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.::




Notes: ::TYPE:Maintenance:NOTE:The description for this entry is generally applicable to XML, but the name includes blind XPath injection which is more closely associated with CWE-643. Therefore this entry might need to be deprecated or converted to a general category - although injection into raw XML is not covered by CWE-643 or CWE-652.::TYPE:Theoretical:NOTE:In vulnerability theory terms, this is a representation-specific case of a Data/Directive Boundary Error.::TYPE:Research Gap:NOTE:Under-reported. This is likely found regularly by third party code auditors, but there are very few publicly reported examples.::