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Validate method parameters arguments to ensure that they fall within the bounds of the method's intended design. This practice ensures that operations on the method's parameters yield valid results. Failure to validate method parameters arguments can result in incorrect calculations, runtime exceptions, violation of class invariants, and inconsistent object state.

Programmers often assume that validation of arguments passed to private methods is unnecessary because such methods cannot be accessed directly by code present outside their enclosing class. This assumption is incorrect. Programming errors often arise when legitimate code behaves in unanticipated ways. For example, a tainted value may propagate from a public API to a private methods via its parameters.

Never use assertions should to validate parameters of {{public}} methods. According to the Java Language Specification \[[JLS 2005|AA. Bibliography#JLS 05]\], Section 14.10 "The {{assert}} Statement"

Along similar lines, assertions should not be used for argument-checking in public methods. Argument-checking is typically part of the contract of a method, and this contract must be upheld whether assertions are enabled or disabled.

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Redundant testing of arguments by both the caller and the callee is a style of defensive programming that is largely discredited within the programming community, in part for reasons of performance. Instead, normal practice requires validation on only one side of each interface.

Caller validation of arguments can result in faster code because the caller may be aware of invariants that prevent invalid values from being passed. Conversely, callee validation of arguments encapsulates the validation code in a single location, reducing the size of the code and raising the likelihood that the validation checks are performed consistently and correctly.

Methods that receive arguments across a trust boundary must perform callee validation of their arguments for safety and security reasons. This precaution applies to all public methods of a library. Other methods, including private methods, should validate arguments that are both untrusted and unvalidated when those arguments may propagate from a public method via its arguments.

When defensive copying is necessary, make the defensive copies before parameter argument validation; , and validate the copies rather than the original parameters. See guideline SER07arguments (see SER06-J. Make defensive copies of private mutable components during deserialization for additional information).

Noncompliant Code Example

The method AbsAddIn this noncompliant code example, setState() computes and returns the sum of the absolute value of parameters x and y. It lacks parameter validation. Consequently, it can produce incorrect results either due to integer overflow or when either or both of its arguments are Math.abs(Integer.MIN_VALUE). and useState() fail to validate their arguments. A malicious caller could pass an invalid state to the library, consequently corrupting the library and exposing a vulnerability.

publicprivate staticObject intmyState AbsAdd(int x, int y) {
  return Math.abs(x) + Math.abs(y);
}
AbsAdd(Integer.MIN_VALUE, 1);

Noncompliant Code Example

This noncompliant code example uses assertions to validate arguments of a public method.

public static int AbsAdd(int x, int y= null;

// Sets some internal state in the library
void setState(Object state) {
  assert xmyState != Integer.MIN_VALUEstate;
}

// Performs assertsome yaction != Integer.MIN_VALUE;
  assert ((x <= Integer.MAX_VALUE - y));
  assert ((x >= Integer.MIN_VALUE - y));
  return Math.abs(x) + Math.abs(y);
}
using the state passed earlier
void useState() {
  // Perform some action here
}

Such vulnerabilities are particularly severe when the internal state contains or refers to sensitive or system-critical dataThe conditions checked by the assertions are reasonable. However, the validation code is omitted when executing with assertions turned off.

Compliant Solution

This compliant solution both validates the method arguments by ensuring that values passed to Math.abs() exclude Integer.MIN_VALUE and also by checking for integer overflow. Alternatively, the addition could be performed using type long and the result of the addition stored in a local variable of type long. This alternate implementation would require a check to ensure that the resulting long can be represented in the range of the type int. Failure of this latter check would indicate that an int version of the addition would have overflowedand verifies the internal state before use. This practice promotes consistency in program execution and reduces the potential for vulnerabilities.

public static int AbsAdd(int x, int yprivate Object myState = null;

// Sets some internal state in the library
void setState(Object state) {
  if ((xstate == Integer.MIN_VALUE || y == Integer.MIN_VALUE) ||
    (x>0 && y>0 && (x > Integer.MAX_VALUE - y)) || 
    (x<0 && y<0 && (x < Integer.MIN_VALUE - y)))
      throw new IllegalArgumentException();

  return Math.abs(x) + Math.abs(y);
}

Exceptions

 null) {
    // Handle null state
  }

  // Defensive copy here when state is mutable

  if (isInvalidState(state)) {
    // Handle invalid state
  }
  myState = state;
}

// Performs some action using the state passed earlier
void useState() {
  if (myState == null) {
    // Handle no state (e.g., null) condition
  }
  // ...
}

Exceptions

MET00-J-EX0: Argument MET02-EX1: Parameter validation inside a method may be omitted when the stated contract of a method requires that the caller must validate arguments passed to the method. In this case, the validation must be performed by the caller for all invocations of the method.

MET02MET00-J-EX2EX1: Parameter Argument validation may be omitted for parameters arguments whose type adequately constrains the state of the parameterargument. This constraint should be clearly documented in the code.

This exception may apply to arguments whose values (as permitted by their type) are not necessarily valid but are still correctly handled by the method. In the following code, the arguments x and y are not validated even though their product might not be a valid int. The code is safe because it adequately handles all int values for x and y.

public int product(int x, int y) {
  long result = (long) x * y;
  if (result < Integer.MIN_VALUE || result > Integer.MAX_VALUE) {
    // Handle error
  }
  return (int) result;
}

MET00-J-EX2MET02-EX3: Complete validation of all parameters arguments of all methods may introduce added cost and complexity that exceeds its value for all but the most critical code. See, for example, NUM00-J. Detect or prevent integer overflow exception NUM00-EX2. In such cases, consider parameter argument validation at API boundaries, especially those that may involve interaction with untrusted code.

Risk Assessment

Failure to validate method parameters arguments can result in inconsistent computations, runtime exceptions, and control flow vulnerabilities.

Related

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Guidelines

Bibliography

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Search for vulnerabilities resulting from the violation of this guideline on the CERT website.

Bibliography

\[[Bloch 2008|AA. Bibliography#Bloch 08]\] Item 38: Check parameters for validity
\[[Daconta 2003|AA. Bibliography#Daconta 03]\] Item 7: My Assertions Are Not Gratuitous
\[[ESA 2005|AA. Bibliography#ESA 05]\] Rule 68: Explicitly check method parameters for validity, and throw an adequate exception in case they are not valid. Do not use the assert statement for this purpose
\[[JLS 2005|AA. Bibliography#JLS 05]\] 14.10 The assert Statement

MET00-J. Avoid ambiguous uses of overloading      05. Methods (MET)      Image Modified