CWE-476: NULL Pointer Dereference
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This table specifies different individual consequences
associated with the weakness. The Scope identifies the application security area that is
violated, while the Impact describes the negative technical impact that arises if an
adversary succeeds in exploiting this weakness. The Likelihood provides information about
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consequences in the list. For example, there may be high likelihood that a weakness will be
exploited to achieve a certain impact, but a low likelihood that it will be exploited to
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This table shows the weaknesses and high level categories that are related to this
weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to
similar items that may exist at higher and lower levels of abstraction. In addition,
relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user
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Relevant to the view "Research Concepts" (CWE-1000)
This table shows the weaknesses and high level categories that are related to this
weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to
similar items that may exist at higher and lower levels of abstraction. In addition,
relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user
may want to explore.
Relevant to the view "Software Development" (CWE-699)
This table shows the weaknesses and high level categories that are related to this
weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to
similar items that may exist at higher and lower levels of abstraction. In addition,
relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user
may want to explore.
Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
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This listing shows possible areas for which the given
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may be for specific named Languages, Operating Systems, Architectures, Paradigms,
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or a class of such platforms. The platform is listed along with how frequently the given
weakness appears for that instance.
Languages C (Undetermined Prevalence) C++ (Undetermined Prevalence) Java (Undetermined Prevalence) C# (Undetermined Prevalence) Go (Undetermined Prevalence) Example 1 While there are no complete fixes aside from conscientious programming, the following steps will go a long way to ensure that NULL pointer dereferences do not occur. (good code)
if (pointer1 != NULL) {
/* make use of pointer1 */ /* ... */ When working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the if statement; and unlock when it has finished. Example 2 This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer. (bad code)
Example Language: C
void host_lookup(char *user_supplied_addr){
struct hostent *hp;
in_addr_t *addr; char hostname[64]; in_addr_t inet_addr(const char *cp); /*routine that ensures user_supplied_addr is in the right format for conversion */ validate_addr_form(user_supplied_addr); addr = inet_addr(user_supplied_addr); hp = gethostbyaddr( addr, sizeof(struct in_addr), AF_INET); strcpy(hostname, hp->h_name); If an attacker provides an address that appears to be well-formed, but the address does not resolve to a hostname, then the call to gethostbyaddr() will return NULL. Since the code does not check the return value from gethostbyaddr (CWE-252), a NULL pointer dereference (CWE-476) would then occur in the call to strcpy(). Note that this code is also vulnerable to a buffer overflow (CWE-119). Example 3 In the following code, the programmer assumes that the system always has a property named "cmd" defined. If an attacker can control the program's environment so that "cmd" is not defined, the program throws a NULL pointer exception when it attempts to call the trim() method. (bad code)
Example Language: Java
String cmd = System.getProperty("cmd");
cmd = cmd.trim(); Example 4 This Android application has registered to handle a URL when sent an intent: (bad code)
Example Language: Java
... IntentFilter filter = new IntentFilter("com.example.URLHandler.openURL"); MyReceiver receiver = new MyReceiver(); registerReceiver(receiver, filter); ... public class UrlHandlerReceiver extends BroadcastReceiver { @Override
public void onReceive(Context context, Intent intent) { if("com.example.URLHandler.openURL".equals(intent.getAction())) {
String URL = intent.getStringExtra("URLToOpen");
int length = URL.length(); ... } 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. Example 5 Consider the following example of a typical client server exchange. The HandleRequest function is intended to perform a request and use a defer to close the connection whenever the function returns. (bad code)
Example Language: Go
func HandleRequest(client http.Client, request *http.Request) (*http.Response, error) {
response, err := client.Do(request)
}defer response.Body.Close() if err != nil {
return nil, err
}... If a user supplies a malformed request or violates the client policy, the Do method can return a nil response and a non-nil err. This HandleRequest Function evaluates the close before checking the error. A deferred call's arguments are evaluated immediately, so the defer statement panics due to a nil response.
This MemberOf Relationships table shows additional CWE Categories and Views that
reference this weakness as a member. This information is often useful in understanding where a
weakness fits within the context of external information sources.
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