NULL Pointer Dereference
|ID: 476||Date: (C)2012-05-14 (M)2018-12-12|
|Type: weakness||Status: DRAFT|
|Abstraction Type: Base|
A NULL pointer dereference occurs when the application
dereferences a pointer that it expects to be valid, but is NULL, typically
causing a crash or exit.
Extended DescriptionNULL pointer dereference issues can occur through a number of flaws,
including race conditions, and simple programming omissions.
Likelihood of Exploit: Medium
Applicable PlatformsLanguage: CLanguage: C++Language: JavaLanguage: .NET
Time Of Introduction
Related Attack Patterns
|Availability ||DoS: crash / exit /
restart ||NULL pointer dereferences usually result in the failure of the process
unless exception handling (on some platforms) is available and
implemented. Even when exception handling is being used, it can still be
very difficult to return the software to a safe state of
|IntegrityConfidentialityAvailability ||Execute unauthorized code or
commands ||In very rare circumstances and environments, code execution is
|Automated Dynamic Analysis ||This weakness can be detected using dynamic tools and techniques that
interact with the software using large test suites with many diverse
inputs, such as fuzz testing (fuzzing), robustness testing, and fault
injection. The software's operation may slow down, but it should not
become unstable, crash, or generate incorrect results. ||Moderate || |
|Manual Dynamic Analysis ||Identify error conditions that are not likely to occur during normal
usage and trigger them. For example, run the program under low memory
conditions, run with insufficient privileges or permissions, interrupt a
transaction before it is completed, or disable connectivity to basic
network services such as DNS. Monitor the software for any unexpected
behavior. If you trigger an unhandled exception or similar error that
was discovered and handled by the application's environment, it may
still indicate unexpected conditions that were not handled by the
application itself. || || |
|Implementation || ||If all pointers that could have been modified are sanity-checked
previous to use, nearly all NULL pointer dereferences can be
prevented. || || |
|Requirements || ||The choice could be made to use a language that is not susceptible to
these issues. || || |
|Implementation || ||Check the results of all functions that return a value and verify that
the value is non-null before acting upon it. ||Moderate ||Checking the return value of the function will typically be
sufficient, however beware of race conditions (CWE-362) in a concurrent
environment.This solution does not handle the use of improperly initialized
variables (CWE-665). |
|Architecture and Design || ||Identify all variables and data stores that receive information from
external sources, and apply input validation to make sure that they are
only initialized to expected values. || || |
|Implementation || ||Explicitly initialize all your variables and other data stores, either
during declaration or just before the first usage. || || |
|Testing || ||Use automated static analysis tools that target this type of weakness.
Many modern techniques use data flow analysis to minimize the number of
false positives. This is not a perfect solution, since 100% accuracy and
coverage are not feasible. || || |
|CWE-476 ChildOf CWE-890 ||Category ||CWE-888 || |
Demonstrative Examples (Details)
- 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.
- 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. (Demonstrative Example Id DX-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.
- CVE-2005-3274 : race condition causes a table to be corrupted if a timer activates while it is being modified, leading to resultant NULL dereference; also involves locking.
- CVE-2002-1912 : large number of packets leads to NULL dereference
- CVE-2005-0772 : packet with invalid error status value triggers NULL dereference
- CVE-2009-4895 : chain: race condition for an argument value, possibly resulting in NULL dereference
- CVE-2009-3547 : chain: race condition might allow resource to be released before operating on it, leading to NULL dereference
- CVE-2009-3620 : chain: some unprivileged ioctls do not verify that a structure has been initialized before invocation, leading to NULL dereference
- CVE-2009-2698 : chain: IP and UDP layers each track the same value with different mechanisms that can get out of sync, possibly resulting in a NULL dereference
- CVE-2009-2692 : chain: uninitialized function pointers can be dereferenced allowing code execution
- CVE-2009-0949 : chain: improper initialization of memory can lead to NULL dereference
- CVE-2008-3597 : chain: game server can access player data structures before initialization has happened leading to NULL dereference
- CVE-2008-5183 : chain: unchecked return value can lead to NULL dereference
- CVE-2004-0079 : SSL software allows remote attackers to cause a denial of service (crash) via a crafted SSL/TLS handshake that triggers a null dereference.
- CVE-2004-0365 : Network monitor allows remote attackers to cause a denial of service (crash) via a malformed RADIUS packet that triggers a null dereference.
- CVE-2003-1013 : Network monitor allows remote attackers to cause a denial of service (crash) via a malformed Q.931, which triggers a null dereference.
- CVE-2003-1000 : Chat client allows remote attackers to cause a denial of service (crash) via a passive DCC request with an invalid ID number, which causes a null dereference.
- CVE-2004-0389 : Server allows remote attackers to cause a denial of service (crash) via malformed requests that trigger a null dereference.
- CVE-2004-0119 : OS allows remote attackers to cause a denial of service (crash from null dereference) or execute arbitrary code via a crafted request during authentication protocol selection.
- CVE-2004-0458 : Game allows remote attackers to cause a denial of service (server crash) via a missing argument, which triggers a null pointer dereference.
- CVE-2002-0401 : Network monitor allows remote attackers to cause a denial of service (crash) or execute arbitrary code via malformed packets that cause a NULL pointer dereference.
For more examples, refer to CVE relations in the bottom box.
White Box DefinitionsA weakness where the code path has:1. start statement that assigns a null value to the pointer2. end statement that dereferences a pointer3. the code path does not contain any other statement that assigns
value to the pointer
Black Box Definitions None
|7 Pernicious Kingdoms || ||Null Dereference || |
|CLASP || ||Null-pointer dereference || |
|PLOVER || ||Null Dereference (Null Pointer Dereference) || |
|OWASP Top Ten 2004 ||A9 ||Denial of Service ||CWE_More_Specific |
|CERT C Secure Coding ||EXP34-C ||Ensure a null pointer is not dereferenced || |
|CERT C Secure Coding ||MEM32-C ||Detect and handle memory allocation errors || |
|CERT C++ Secure Coding ||EXP34-CPP ||Ensure a null pointer is not dereferenced || |
|CERT C++ Secure Coding ||MEM32-CPP ||Detect and handle memory allocation errors || |