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Introduction

ASoftware softwarecomponents component often containscontain severalmultiple subcomponents that act as subsystems, where each component operates in one or more trusted domains. For example, one component may have access to the file system, but notlack access to the network, while another component canhas access to the network but notlacks access to the file system. Both _distrustfulDistrustful decomposition_ and  _privilege separation_ \[[Dougherty 2009|AA. Bibliography#Dougherty 2009]\]]  are examples of secure design patterns that recommend designing a system using  mutually untrusting subcomponents to reduce reducing the amount of code that runs with special privileges by designing the system using mutually untrusting subcomponents.

When any two subcomponents having different with differing degrees of trust share data, the data is are said to flow across a trust boundary. Because Java allows components under different protection domains to communicate with each other, data can be transmitted across a trust boundary. Furthermore, a Java program can contain both internally developed and third-party code. Data that is are transmitted to or accepted from third-party code also flows flow across a trust boundary.

While software components can obey policies that allow them to transmit data across trust boundaries, they cannot specify the level of trust given to any component. The deployer of the application must define the trust boundaries with the help of a system-wide security policy. A security auditor can use that definition to determine whether the software adequately supports the security objectives of the application.

Any thirdThird-party code should operate in its own security domain and ; any code potentially exported to a third-party — such as libraries — should be deployable in well-defined security domains. The public API of the potentially-exported code can be considered as to be a trust boundary. Data flowing across a trust boundary should be validated if when the publisher does not provide any lacks guarantees of validation. A subscriber or client need not provide any validation if may omit validation when the data flowing into its trust boundary is appropriate for use as is. In all other cases, inbound data must be validated.???

Data

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Data Output

If data must be sent to a component in a different protection domain, the sender must ensure that the data is suitable to the receiver's trust boundary by filtering out any sensitive information. For instance, if malicious code manages to infiltrate a system, many attacks will be futile if the system's output is appropriately escaped and encoded. Refer to the guideline IDS04-J. Properly encode or escape output for more details.

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Like trust boundaries, the question of what information is sensitive is resolved by the system's security policy. A component cannot define which information is sensitive; it can only provide support for handling information that may potentially be declared sensitive by the system administrator.

Java software components might provide many opportunities to output sensitive information. Several rules address the mitigation of sensitive information disclosure, including EXC06-J. Do not allow exceptions to expose sensitive information and FIO08-J. Do not log sensitive information.

Data Input

Data that is received by a component from a source outside the component's trust boundary may, in fact, be malicious. The program must therefore take steps to ensure that the data is are both genuine and appropriate.

These steps can include the following:

Validation, in the broadest sense, is the process of ensuring that input data falls fall within the expected range domain of valid program input. For example, not only must method arguments must conform not only to the type and numeric range requirements of a method or subsystem, but also they must contain data that conforms conform to the required input invariants for that method.

Sanitization: In many cases, the data may be fed passed directly to some subsystem. Data sanitization is the process of ensuring that data conforms conform to the requirements of the subsystem to which it they are passed. Sanitization also involves ensuring that data also conforms conform to any security-related requirements regarding leaking or exposure of sensitive data when it is output across a trust boundary. Refer to the related guideline IDS01-J. Sanitize before processing or storing user input for more details on data sanitization. Data sanitization and input validation may coexist and complement each other.

Canonicalization and Normalization: Canonicalization is the process of lossless reduction of the input to its equivalent simplest known form. Normalization is the process of lossy conversion of the input data to its the simplest known (and anticipated) form. Canonicalization and normalization must occur before validation to prevent attackers from exploiting the validation routine to strip away illegal characters and thus construct constructing a forbidden (and potentially malicious) character sequence. Refer to the guideline IDS02-J. Validate strings after performing normalization for more details. In addition, ensure that normalization is performed only on fully assembled user input. Never normalize partial input or combine normalized input with non-normalized input.

For example, POSIX file systems provide a syntax for expressing file names on the system using paths. A path is a string which indicates how to find any file by starting at a particular directory (usually the current working directory), and traversing down directories until the file is found. A path is canonical if it contains no Canonical paths lack both symbolic links , and no special entries , such as '.' or '..'; as these , which are handled specially on POSIX systems. Every Each file accessible from a directory has exactly one canonical path, along with many non-canonical paths.

Many rules address proper filtering of untrusted input, especially when such input is passed to a complex subsystem. For example, see IDS08-J. Prevent XML Injection.

Data Output

When data must be sent to a component in a different trust domain, the sender must ensure that the data is suitable for the receiver's trust boundary by filtering out any sensitive information. For instance, if malicious code manages to infiltrate a system, many attacks will be rendered ineffective if the system's output is appropriately escaped and encoded. Refer to the guideline IDS04-J. Properly encode or escape output for more details.

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Like trust boundaries, the system's security policy determines which information is sensitive. A component cannot define which information is sensitive; it can only provide support for handling information that may potentially be declared sensitive by the system administrator.

Java software components provide many opportunities to output sensitive information. Several rules address the mitigation of sensitive information disclosure, including EXC06-J. Do not allow exceptions to expose sensitive information and FIO08-J. Do not log sensitive information.

Guidelines

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