Difference between revisions of "Null Dereference"

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==Abstract==
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=Description=
 
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The program can potentially dereference a null pointer, thereby raising a NullPointerException. Null pointer errors are usually the result of one or more programmer assumptions being violated. Most null pointer issues result in general software reliability problems, but if an attacker can intentionally trigger a null pointer dereference, the attacker might be able to use the resulting exception to bypass security logic or to cause the application to reveal debugging information that will be valuable in planning subsequent attacks.
The program can potentially dereference a null pointer, thereby raising a NullPointerException.
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==Description==
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Null pointer errors are usually the result of one or more programmer assumptions being violated.
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Most null pointer issues result in general software reliability problems, but if an attacker can intentionally trigger a null pointer dereference, the attacker might be able to use the resulting exception to bypass security logic or to cause the application to reveal debugging information that will be valuable in planning subsequent attacks.
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==Examples ==
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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.
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String cmd = System.getProperty("cmd");
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cmd = cmd.trim();
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==Related Threats==
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==Related Attacks==
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==Related Vulnerabilities==
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==Related Countermeasures==
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==Categories==
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[[Category:Code Quality Vulnerability]]
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[[Category:Java]]
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[[Category:Implementation]]
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[[Category:Code Snippet]]
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{{Template:Vulnerability}}
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{{Template:SecureSoftware}}
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==Overview==
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A null-pointer dereference takes place when a pointer with a value of NULL is used as though it pointed to a valid memory area.
 
A null-pointer dereference takes place when a pointer with a value of NULL is used as though it pointed to a valid memory area.
  
==Consequences ==
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Null-pointer dereferences, while common, can generally be found and corrected in a simple way. They will always result in the crash of the process, unless exception handling (on some platforms) is invoked, and even then, little can be done to salvage the process.
  
* Availability: Null-pointer dereferences invariably result in the failure of the process.
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= Consequences =
  
==Exposure period ==
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* Availability: Null-pointer dereferences invariably result in the failure of the process.
  
* Requirements specification: The choice could be made to use a language that is not susceptible to these issues.
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= Exposure period =
  
* Implementation: Proper sanity checks at implementation time can serve to prevent null-pointer dereferences
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* Requirements specification: The choice could be made to use a language that is not susceptible to these issues.
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* Implementation: Proper sanity checks at implementation time can serve to prevent null-pointer dereferences
  
==Platform ==
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= Platform =
  
* Languages: C, C++, Assembly
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* Languages: C, C++, Java, Assembly
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* Platforms: All
  
* Platforms: All
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= Examples =
  
==Required resources ==
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== Example 1 ==
  
Any
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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.
  
==Severity ==
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String cmd = System.getProperty("cmd");
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cmd = cmd.trim();
  
Medium
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== Example 2 ==
  
==Likelihood  of exploit ==
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Null-pointer dereference issues can occur through a number of flaws, including race conditions and simple programming omissions. While there are no complete fixes aside from contentious programming, the following steps will go a long way to ensure that null-pointer dereferences do not occur.
 
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Medium
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==Avoidance and mitigation ==
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* Requirements specification: The choice could be made to use a language that is not susceptible to these issues.
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* Implementation: If all pointers that could have been modified are sanity-checked previous to use, nearly all null-pointer dereferences can be prevented.
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==Discussion ==
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Null-pointer dereferences, while common, can generally be found and corrected in a simply way. They will always result in the crash of the process - unless exception handling (on some platforms) in invoked, and even then, little can be done to salvage the process.
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==Examples ==
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Null-pointer dereference issue can occur through a number of flaws, including race conditions, and simple programming omissions. While there are no complete fixes aside from contentious programming, the following steps will go a long way to ensure that null-pointer dereferences do not occur.
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Before using a pointer, ensure that it is not equal to NULL:
 
Before using a pointer, ensure that it is not equal to NULL:
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If you are working with a multi-threaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the if statement; and unlock when it has finished.
 
If you are working with a multi-threaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the if statement; and unlock when it has finished.
  
==Related problems ==
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= Related [[Vulnerabilities]] =
  
* [[Miscalculated null termination]]
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* [[Miscalculated null termination]]
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* [[State synchronization error]]
  
* [[State synchronization error]]
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= Related [[Controls]] =
  
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* Requirements specification: The choice could be made to use a language that is not susceptible to these issues.
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* Implementation: If all pointers that could have been modified are sanity-checked previous to use, nearly all null-pointer dereferences can be prevented.
  
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= References =
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* [http://cwe.mitre.org/data/definitions/79.html CWE 79].
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* http://www.link1.com
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* [http://www.link2.com Title for the link2]
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[[Category:Code Quality Vulnerability]]
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[[Category:Java]]
 
[[Category:Vulnerability]]
 
[[Category:Vulnerability]]
[[Category:Range and Type Error Vulnerability]]
 
[[Category:OWASP_CLASP_Project]]
 
[[Category:Code Snippet]]
 
[[Category:C]]
 

Latest revision as of 13:39, 5 April 2014

Last revision (mm/dd/yy): 04/5/2014

Description

The program can potentially dereference a null pointer, thereby raising a NullPointerException. Null pointer errors are usually the result of one or more programmer assumptions being violated. Most null pointer issues result in general software reliability problems, but if an attacker can intentionally trigger a null pointer dereference, the attacker might be able to use the resulting exception to bypass security logic or to cause the application to reveal debugging information that will be valuable in planning subsequent attacks.

A null-pointer dereference takes place when a pointer with a value of NULL is used as though it pointed to a valid memory area.

Null-pointer dereferences, while common, can generally be found and corrected in a simple way. They will always result in the crash of the process, unless exception handling (on some platforms) is invoked, and even then, little can be done to salvage the process.

Consequences

  • Availability: Null-pointer dereferences invariably result in the failure of the process.

Exposure period

  • Requirements specification: The choice could be made to use a language that is not susceptible to these issues.
  • Implementation: Proper sanity checks at implementation time can serve to prevent null-pointer dereferences

Platform

  • Languages: C, C++, Java, Assembly
  • Platforms: All

Examples

Example 1

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.

String cmd = System.getProperty("cmd"); cmd = cmd.trim();

Example 2

Null-pointer dereference issues can occur through a number of flaws, including race conditions and simple programming omissions. While there are no complete fixes aside from contentious programming, the following steps will go a long way to ensure that null-pointer dereferences do not occur.

Before using a pointer, ensure that it is not equal to NULL:

if (pointer1 != NULL) {
  /* make use of pointer1 */
  /* ... */
}

When freeing pointers, ensure they are not set to NULL, and be sure to set them to NULL once they are freed:

if (pointer1 != NULL) {
  free(pointer1);
  pointer1 = NULL;
}

If you are working with a multi-threaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the if statement; and unlock when it has finished.

Related Vulnerabilities

Related Controls

  • Requirements specification: The choice could be made to use a language that is not susceptible to these issues.
  • Implementation: If all pointers that could have been modified are sanity-checked previous to use, nearly all null-pointer dereferences can be prevented.

References