Poor code quality leads to unpredictable behavior. From a user's perspective that often manifests itself as poor usability. For an attacker it provides an opportunity to stress the system in unexpected ways.
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var file:File = new File(directoryName + "\\" + fileName);
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FileStream f = File.Create(directoryName + "\\" + fileName);
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File file = new File(directoryName + "\\" + fileName);
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os.open(directoryName + "\\" + fileName);
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<script> tag.
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public String tagProcessor(String tag){
if (tag.toUpperCase().equals("SCRIPT")){
return null;
}
//does not contain SCRIPT tag, keep processing input
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}
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Example 1 is that java.lang.String.toUpperCase() when used without a locale uses the rules of the default locale. Using the Turkish locale "title".toUpperCase() returns "T\u0130TLE", where "\u0130" is the "LATIN CAPITAL LETTER I WITH DOT ABOVE" character. This can lead to unexpected results, such as in Example 1 where this will prevent the word "script" from being caught by this validation, potentially leading to a Cross-Site Scripting vulnerability.
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import java.sql.PreparedStatement;
import com.sap.sql.NativeSQLAccess;
String mssOnlyStmt = "...";
// variant 1
PreparedStatement ps =
NativeSQLAccess.prepareNativeStatement(
conn, mssOnlyStmt);
. . .
// variant 2
Statement stmt =
NativeSQLAccess.createNativeStatement(conn);
int result = stmt.execute(mssOnlyStmt);
. . .
// variant 3
CallableStatement cs =
NativeSQLAccess.prepareNativeCall(
conn, mssOnlyStmt);
. . .
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public class Box{
public int area;
public static final int width = 10;
public static final Box box = new Box();
public static final int height = (int) (Math.random() * 100);
public Box(){
area = width * height;
}
...
}
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Example 1, the developer would expect that box.area would be a random integer that happens to be a multiple of 10, due to width being equal to 10. In reality however, this will always have a hardcoded value of 0. Static final fields declared with a compile-time constant are initialized first, and then each one is executed in order. This means that since height is not a compile-time constant, it is declared after the declaration of box, and therefore the constructor is called prior to the field height being initialized.
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class Foo{
public static final int f = Bar.b - 1;
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}
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class Bar{
public static final int b = Foo.f + 1;
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}
This example is perhaps easier to identify, but would be dependent on which class is loaded first by the JVM. In this exampleFoo.fcould be either -1 or 0, andBar.bcould be either 0 or 1.
null before checking if the pointer is null. Dereference-after-check errors occur when a program makes an explicit check for null, but proceeds to dereference the pointer when it is known to be null. Errors of this type are often the result of a typo or programmer oversight. A dereference-after-store error occurs when a program explicitly sets a pointer to null and dereferences it later. This error is often the result of a programmer initializing a variable to null when it is declared.foo is null and subsequently dereferences it erroneously. If foo is null when it is checked in the if statement, then a null dereference occurs, which causes a null-pointer exception.Example 2: In the following code, the programmer assumes that the variable
if (foo is null) {
foo.SetBar(val);
...
}
foo is not null and confirms this assumption by dereferencing the object. However, the programmer later contradicts the assumption by checking foo against null. If foo can be null when it is checked in the if statement then it can also be null when it is dereferenced and might cause a null-pointer exception. Either the dereference is unsafe or the subsequent check is unnecessary.Example 3: In the following code, the programmer explicitly sets the variable
foo.SetBar(val);
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if (foo is not null) {
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}
foo to null. Later, the programmer dereferences foo before checking the object for a null value.
Foo foo = null;
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foo.SetBar(val);
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}
null before checking if the pointer is null. Dereference-after-check errors occur when a program makes an explicit check for null, but proceeds to dereference the pointer when it is known to be null. Errors of this type are often the result of a typo or programmer oversight. A dereference-after-store error occurs when a program explicitly sets a pointer to null and dereferences it later. This error is often the result of a programmer initializing a variable to null when it is declared.ptr is not NULL. That assumption is made explicit when the programmer dereferences the pointer. This assumption is later contradicted when the programmer checks ptr against NULL. If ptr can be NULL when it is checked in the if statement then it can also be NULL when it dereferenced and may cause a segmentation fault.Example 2: In the following code, the programmer confirms that the variable
ptr->field = val;
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if (ptr != NULL) {
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}
ptr is NULL and subsequently dereferences it erroneously. If ptr is NULL when it is checked in the if statement, then a null dereference will occur, thereby causing a segmentation fault.Example 3: In the following code, the programmer forgets that the string
if (ptr == null) {
ptr->field = val;
...
}
'\0' is actually 0 or NULL, thereby dereferencing a null-pointer and causing a segmentation fault.Example 4: In the following code, the programmer explicitly sets the variable
if (ptr == '\0') {
*ptr = val;
...
}
ptr to NULL. Later, the programmer dereferences ptr before checking the object for a null value.
*ptr = NULL;
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ptr->field = val;
...
}
null, but proceeds to dereference the object when it is known to be null. Errors of this type are often the result of a typo or programmer oversight.foo is null and subsequently dereferences it erroneously. If foo is null when it is checked in the if statement, then a null dereference will occur, thereby causing a null-pointer exception.
if (foo == null) {
foo.setBar(val);
...
}
require.
function withdrawWinnings() {
require(uint32(msg.sender) == 0);
_sendWinnings();
}
function _sendWinnings() {
msg.sender.transfer(this.balance);
}
assert to check that the balance of the Lock contract instance is a specific value (msg.value).
contract Lock {
constructor (address owner, uint256 unlockTime) public payable {
...
}
}
contract Lockdrop {
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function lock(...) {
uint256 eth = msg.value;
address owner = msg.sender;
uint256 unlockTime = unlockTimeForTerm(term);
Lock lockAddr = (new Lock).value(eth)(owner, unlockTime);
assert(address(lockAddr).balance == msg.value);
}
}