Which tool should an application developer use to help identify input validation vulnerabilities?
|
Weakness ID: 20 Abstraction: ClassStructure: Simple
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
Input validation is a frequently-used technique for checking potentially dangerous inputs in order to ensure that the inputs are safe for processing within the code, or when communicating with other components. When software does not validate input properly, an attacker is able to craft the input in a form that is not expected by the rest of the application. This will lead to parts of the system receiving unintended input, which may result in altered control flow, arbitrary control of a resource, or arbitrary code execution. Input validation is not the only technique for processing input, however. Other techniques attempt to transform potentially-dangerous input into something safe, such as filtering (CWE-790) - which attempts to remove dangerous inputs - or encoding/escaping (CWE-116), which attempts to ensure that the input is not misinterpreted when it is included in output to another component. Other techniques exist as well (see CWE-138 for more examples.) Input validation can be applied to:
Data can be simple or structured. Structured data can be composed of many nested layers, composed of combinations of metadata and raw data, with other simple or structured data. Many properties of raw data or metadata may need to be validated upon entry into the code, such as:
Implied or derived properties of data must often be calculated or inferred by the code itself. Errors in deriving properties may be considered a contributing factor to improper input validation. Note that "input validation" has very different meanings to different people, or within different classification schemes. Caution must be used when referencing this CWE entry or mapping to it. For example, some weaknesses might involve inadvertently giving control to an attacker over an input when they should not be able to provide an input at all, but sometimes this is referred to as input validation. Finally, it is important to emphasize that the distinctions between input validation and output escaping are often blurred, and developers must be careful to understand the difference, including how input validation is not always sufficient to prevent vulnerabilities, especially when less stringent data types must be supported, such as free-form text. Consider a SQL injection scenario in which a person's last name is inserted into a query. The name "O'Reilly" would likely pass the validation step since it is a common last name in the English language. However, this valid name cannot be directly inserted into the database because it contains the "'" apostrophe character, which would need to be escaped or otherwise transformed. In this case, removing the apostrophe might reduce the risk of SQL injection, but it would produce incorrect behavior because the wrong name would be recorded.
Languages Class: Language-Independent (Often Prevalent)
Example 1 This example demonstrates a shopping interaction in which the user is free to specify the quantity of items to be purchased and a total is calculated. (bad code) Example Language: Java ... The user has no control over the price variable, however the code does not prevent a negative value from being specified for quantity. If an attacker were to provide a negative value, then the user would have their account credited instead of debited. Example 2 This example asks the user for a height and width of an m X n game board with a maximum dimension of 100 squares. (bad code) Example Language: C ... int m,n, error; die("No integer passed: Die evil hacker!\n"); } die("No integer passed: Die evil hacker!\n"); } die("Value too large: Die evil hacker!\n"); } While this code checks to make sure the user cannot specify large, positive integers and consume too much memory, it does not check for negative values supplied by the user. As a result, an attacker can perform a resource consumption (CWE-400) attack against this program by specifying two, large negative values that will not overflow, resulting in a very large memory allocation (CWE-789) and possibly a system crash. Alternatively, an attacker can provide very large negative values which will cause an integer overflow (CWE-190) and unexpected behavior will follow depending on how the values are treated in the remainder of the program. Example 3 The following example shows a PHP application in which the programmer attempts to display a user's birthday and homepage. (bad code) Example Language: PHP $birthday = $_GET['birthday']; The programmer intended for $birthday to be in a date format and $homepage to be a valid URL. However, since the values are derived from an HTTP request, if an attacker can trick a victim into clicking a crafted URL with } } This example attempts to build a list from a user-specified value, and even checks to ensure a non-negative value is supplied. If, however, a 0 value is provided, the code will build an array of size 0 and then try to store a new Widget in the first location, causing an exception to be thrown. Example 5 This Android application has registered to handle a URL when sent an intent: (bad code) Example Language: Java ...
public class UrlHandlerReceiver extends BroadcastReceiver { @Override if("com.example.URLHandler.openURL".equals(intent.getAction())) { String URL = intent.getStringExtra("URLToOpen"); ...
} } The application assumes the URL will always be included in the intent. When the URL is not present, the call to getStringExtra() will return null, thus causing a null pointer exception when length() is called.
Maintenance As of 2020, this entry is used more often than preferred, and it is a source of frequent confusion. It is being actively modified for CWE 4.1 and subsequent versions. Maintenance Concepts such as validation, data transformation, and neutralization are being refined, so relationships between CWE-20 and other entries such as CWE-707 may change in future versions, along with an update to the Vulnerability Theory document. Maintenance Input validation - whether missing or incorrect - is such an essential and widespread part of secure development that it is implicit in many different weaknesses. Traditionally, problems such as buffer overflows and XSS have been classified as input validation problems by many security professionals. However, input validation is not necessarily the only protection mechanism available for avoiding such problems, and in some cases it is not even sufficient. The CWE team has begun capturing these subtleties in chains within the Research Concepts view (CWE-1000), but more work is needed. Relationship CWE-116 and CWE-20 have a close association because, depending on the nature of the structured message, proper input validation can indirectly prevent special characters from changing the meaning of a structured message. For example, by validating that a numeric ID field should only contain the 0-9 characters, the programmer effectively prevents injection attacks. Terminology The "input validation" term is extremely common, but it is used in many different ways. In some cases its usage can obscure the real underlying weakness or otherwise hide chaining and composite relationships. Some people use "input validation" as a general term that covers many different neutralization techniques for ensuring that input is appropriate, such as filtering, canonicalization, and escaping. Others use the term in a more narrow context to simply mean "checking if an input conforms to expectations without changing it." CWE uses this more narrow interpretation.
More information is available — Please select a different filter. |
