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CWE-469: Use of Pointer Subtraction to Determine Size

Weakness ID: 469
Abstraction: Base
Structure: Simple
Status: Draft
Presentation Filter:
+ Description
The application subtracts one pointer from another in order to determine size, but this calculation can be incorrect if the pointers do not exist in the same memory chunk.
+ Relationships

The table(s) below 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 "Research Concepts" (CWE-1000)
ChildOfClassClass682Incorrect Calculation
+ Relevant to the view "Development Concepts" (CWE-699)
MemberOfCategoryCategory465Pointer Issues
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

+ Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.


C (Undetermined Prevalence)

C++ (Undetermined Prevalence)

+ Common Consequences

The table below 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 how likely the specific consequence is expected to be seen relative to the other 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 achieve a different impact.

Access Control

Technical Impact: Execute Unauthorized Code or Commands; Gain Privileges or Assume Identity

There is the potential for arbitrary code execution with privileges of the vulnerable program.
+ Likelihood Of Exploit
+ Demonstrative Examples

Example 1

The following example contains the method size that is used to determine the number of nodes in a linked list. The method is passed a pointer to the head of the linked list.

(bad code)
Example Language:
struct node {
int data;
struct node* next;

// Returns the number of nodes in a linked list from
// the given pointer to the head of the list.

int size(struct node* head) {
struct node* current = head;
struct node* tail;
while (current != NULL) {
tail = current;
current = current->next;

return tail - head;

// other methods for manipulating the list


However, the method creates a pointer that points to the end of the list and uses pointer subtraction to determine the number of nodes in the list by subtracting the tail pointer from the head pointer. There no guarantee that the pointers exist in the same memory area, therefore using pointer subtraction in this way could return incorrect results and allow other unintended behavior. In this example a counter should be used to determine the number of nodes in the list, as shown in the following code.

(good code)
Example Language:


int size(struct node* head) {
struct node* current = head;
int count = 0;
while (current != NULL) {
current = current->next;

return count;

+ Potential Mitigations

Phase: Implementation

Save an index variable. This is the recommended solution. Rather than subtract pointers from one another, use an index variable of the same size as the pointers in question. Use this variable to "walk" from one pointer to the other and calculate the difference. Always sanity check this number.
+ Memberships
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.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CLASPImproper pointer subtraction
CERT C Secure CodingARR36-CExactDo not subtract or compare two pointers that do not refer to the same array
Software Fault PatternsSFP7Faulty Pointer Use
+ Content History
Submission DateSubmitterOrganization
Modification DateModifierOrganization
2008-07-01Eric DalciCigital
updated Time_of_Introduction
2008-08-01KDM Analytics
added/updated white box definitions
2008-09-08CWE Content TeamMITRE
updated Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings
2008-11-24CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2011-09-13CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITRE
updated Relationships
2012-10-30CWE Content TeamMITRE
updated Demonstrative_Examples, Potential_Mitigations
2014-02-18CWE Content TeamMITRE
updated Potential_Mitigations
2014-06-23CWE Content TeamMITRE
updated Other_Notes
2014-07-30CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2017-11-08CWE Content TeamMITRE
updated Demonstrative_Examples, Taxonomy_Mappings, White_Box_Definitions
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Improper Pointer Subtraction

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Page Last Updated: January 18, 2018