Unchecked Return Value to NULL Pointer Dereference
Compound Element ID: 690 (Compound Element Base: Chain)Status: Draft
+ Description

Description Summary

The product does not check for an error after calling a function that can return with a NULL pointer if the function fails, which leads to a resultant NULL pointer dereference.

Extended Description

While unchecked return value weaknesses are not limited to returns of NULL pointers (see the examples in CWE-252), functions often return NULL to indicate an error status. When this error condition is not checked, a NULL pointer dereference can occur.

+ Applicable Platforms




+ Detection Methods

Black Box

This typically occurs in rarely-triggered error conditions, reducing the chances of detection during black box testing.

White Box

Code analysis can require knowledge of API behaviors for library functions that might return NULL, reducing the chances of detection when unknown libraries are used.

+ Demonstrative Examples

Example 1

The code below makes a call to the getUserName() function but doesn't check the return value before dereferencing (which may cause a NullPointerException).

(Bad Code)
Example Language: Java 
String username = getUserName();
if (username.equals(ADMIN_USER)) {

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:
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 */
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 example is also vulnerable to a buffer overflow (see CWE-119).

+ Observed Examples
CVE-2008-1052Large Content-Length value leads to NULL pointer dereference when malloc fails.
CVE-2006-6227Large message length field leads to NULL pointer dereference when malloc fails.
CVE-2006-2555Parsing routine encounters NULL dereference when input is missing a colon separator.
CVE-2003-1054URI parsing API sets argument to NULL when a parsing failure occurs, such as when the Referer header is missing a hostname, leading to NULL dereference.
+ Other Notes

A typical occurrence of this weakness occurs when an application includes user-controlled input to a malloc() call. The related code might be correct with respect to preventing buffer overflows, but if a large value is provided, the malloc() will fail due to insufficient memory. This problem also frequently occurs when a parsing routine expects that certain elements will always be present. If malformed input is provided, the parser might return NULL. For example, strtok() can return NULL.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)Named Chain(s) this relationship pertains toChain(s)
StartsWithWeakness BaseWeakness Base252Unchecked Return Value
Named Chains709
Unchecked Return Value to NULL Pointer Dereference690
ChildOfWeakness ClassWeakness Class20Improper Input Validation
Research Concepts (primary)1000
+ Relevant Properties
  • Validity
+ Content History
Modification DateModifierOrganizationSource
2008-07-01Sean EidemillerCigitalExternal
added/updated demonstrative examples
2008-07-01Eric DalciCigitalExternal
updated Time of Introduction
2008-09-08CWE Content TeamMITREInternal
updated Applicable Platforms, Description, Detection Factors, Relationships, Other Notes
2009-12-28CWE Content TeamMITREInternal
updated Demonstrative Examples