CWE

Common Weakness Enumeration

A community-developed list of SW & HW weaknesses that can become vulnerabilities

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ID

CWE-763: Release of Invalid Pointer or Reference

Weakness ID: 763
Vulnerability Mapping: ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities
Abstraction: BaseBase - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
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+ Description
The product attempts to return a memory resource to the system, but it calls the wrong release function or calls the appropriate release function incorrectly.
+ Extended Description

This weakness can take several forms, such as:

  • The memory was allocated, explicitly or implicitly, via one memory management method and deallocated using a different, non-compatible function (CWE-762).
  • The function calls or memory management routines chosen are appropriate, however they are used incorrectly, such as in CWE-761.
+ Relationships
Section HelpThis 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 "Research Concepts" (CWE-1000)
NatureTypeIDName
ChildOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.404Improper Resource Shutdown or Release
ParentOfVariantVariant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.761Free of Pointer not at Start of Buffer
ParentOfVariantVariant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.762Mismatched Memory Management Routines
Section HelpThis 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)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.399Resource Management Errors
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.465Pointer Issues
Section HelpThis 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)
NatureTypeIDName
ChildOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.404Improper Resource Shutdown or Release
Section HelpThis 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 "CISQ Data Protection Measures" (CWE-1340)
NatureTypeIDName
ChildOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.404Improper Resource Shutdown or Release
+ Modes Of Introduction
Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
PhaseNote
Implementation
+ Common Consequences
Section HelpThis 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 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.
ScopeImpactLikelihood
Integrity
Availability
Confidentiality

Technical Impact: Modify Memory; DoS: Crash, Exit, or Restart; Execute Unauthorized Code or Commands

This weakness may result in the corruption of memory, and perhaps instructions, possibly leading to a crash. If the corrupted memory can be effectively controlled, it may be possible to execute arbitrary code.
+ Demonstrative Examples

Example 1

This code attempts to tokenize a string and place it into an array using the strsep function, which inserts a \0 byte in place of whitespace or a tab character. After finishing the loop, each string in the AP array points to a location within the input string.

(bad code)
Example Language:
char **ap, *argv[10], *inputstring;
for (ap = argv; (*ap = strsep(&inputstring, " \t")) != NULL;)
if (**ap != '\0')
if (++ap >= &argv[10])
break;

/.../
free(ap[4]);

Since strsep is not allocating any new memory, freeing an element in the middle of the array is equivalent to free a pointer in the middle of inputstring.

Example 2

This example allocates a BarObj object using the new operator in C++, however, the programmer then deallocates the object using free(), which may lead to unexpected behavior.

(bad code)
Example Language: C++ 
void foo(){
BarObj *ptr = new BarObj()
/* do some work with ptr here */

...

free(ptr);
}

Instead, the programmer should have either created the object with one of the malloc family functions, or else deleted the object with the delete operator.

(good code)
Example Language: C++ 
void foo(){
BarObj *ptr = new BarObj()
/* do some work with ptr here */

...

delete ptr;
}

Example 3

In this example, the programmer dynamically allocates a buffer to hold a string and then searches for a specific character. After completing the search, the programmer attempts to release the allocated memory and return SUCCESS or FAILURE to the caller. Note: for simplification, this example uses a hard-coded "Search Me!" string and a constant string length of 20.

(bad code)
Example Language:
#define SUCCESS (1)
#define FAILURE (0)

int contains_char(char c){
char *str;
str = (char*)malloc(20*sizeof(char));
strcpy(str, "Search Me!");
while( *str != NULL){
if( *str == c ){

/* matched char, free string and return success */
free(str);
return SUCCESS;
}
/* didn't match yet, increment pointer and try next char */

str = str + 1;
}
/* we did not match the char in the string, free mem and return failure */

free(str);
return FAILURE;
}

However, if the character is not at the beginning of the string, or if it is not in the string at all, then the pointer will not be at the start of the buffer when the programmer frees it.

Instead of freeing the pointer in the middle of the buffer, the programmer can use an indexing pointer to step through the memory or abstract the memory calculations by using array indexing.

(good code)
Example Language:
#define SUCCESS (1)
#define FAILURE (0)

int cointains_char(char c){
char *str;
int i = 0;
str = (char*)malloc(20*sizeof(char));
strcpy(str, "Search Me!");
while( i < strlen(str) ){
if( str[i] == c ){

/* matched char, free string and return success */
free(str);
return SUCCESS;
}
/* didn't match yet, increment pointer and try next char */

i = i + 1;
}
/* we did not match the char in the string, free mem and return failure */

free(str);
return FAILURE;
}

Example 4

Consider the following code in the context of a parsing application to extract commands out of user data. The intent is to parse each command and add it to a queue of commands to be executed, discarding each malformed entry.

(bad code)
Example Language:

//hardcode input length for simplicity
char* input = (char*) malloc(40*sizeof(char));
char *tok;
char* sep = " \t";

get_user_input( input );

/* The following loop will parse and process each token in the input string */

tok = strtok( input, sep);
while( NULL != tok ){
if( isMalformed( tok ) ){

/* ignore and discard bad data */
free( tok );
}
else{
add_to_command_queue( tok );
}
tok = strtok( NULL, sep));
}

While the above code attempts to free memory associated with bad commands, since the memory was all allocated in one chunk, it must all be freed together.

One way to fix this problem would be to copy the commands into a new memory location before placing them in the queue. Then, after all commands have been processed, the memory can safely be freed.

(good code)
Example Language:

//hardcode input length for simplicity
char* input = (char*) malloc(40*sizeof(char));
char *tok, *command;
char* sep = " \t";

get_user_input( input );

/* The following loop will parse and process each token in the input string */

tok = strtok( input, sep);
while( NULL != tok ){
if( !isMalformed( command ) ){

/* copy and enqueue good data */
command = (char*) malloc( (strlen(tok) + 1) * sizeof(char) );
strcpy( command, tok );
add_to_command_queue( command );
}
tok = strtok( NULL, sep));
}

free( input )
+ Observed Examples
ReferenceDescription
function "internally calls 'calloc' and returns a pointer at an index... inside the allocated buffer. This led to freeing invalid memory."
+ Potential Mitigations

Phase: Implementation

Only call matching memory management functions. Do not mix and match routines. For example, when you allocate a buffer with malloc(), dispose of the original pointer with free().

Phase: Implementation

When programming in C++, consider using smart pointers provided by the boost library to help correctly and consistently manage memory.

Phase: Architecture and Design

Strategy: Libraries or Frameworks

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

For example, glibc in Linux provides protection against free of invalid pointers.

Phase: Architecture and Design

Use a language that provides abstractions for memory allocation and deallocation.

Phase: Testing

Use a tool that dynamically detects memory management problems, such as valgrind.
+ Detection Methods

Fuzzing

Fuzz testing (fuzzing) is a powerful technique for generating large numbers of diverse inputs - either randomly or algorithmically - and dynamically invoking the code with those inputs. Even with random inputs, it is often capable of generating unexpected results such as crashes, memory corruption, or resource consumption. Fuzzing effectively produces repeatable test cases that clearly indicate bugs, which helps developers to diagnose the issues.

Effectiveness: High

+ Affected Resources
  • Memory
+ Memberships
Section HelpThis 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.
NatureTypeIDName
MemberOfViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).884CWE Cross-section
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.969SFP Secondary Cluster: Faulty Memory Release
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1237SFP Primary Cluster: Faulty Resource Release
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1399Comprehensive Categorization: Memory Safety
+ Vulnerability Mapping Notes

Usage: ALLOWED

(this CWE ID could be used to map to real-world vulnerabilities)

Reason: Acceptable-Use

Rationale:

This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.

Comments:

Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.
+ Notes

Maintenance

The view-1000 subtree that is associated with this weakness needs additional work. Several entries will likely be created in this branch. Currently the focus is on free() of memory, but delete and other related release routines may require the creation of intermediate entries that are not specific to a particular function. In addition, the role of other types of invalid pointers, such as an expired pointer, i.e. CWE-415 Double Free and release of uninitialized pointers, related to CWE-457.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
Software Fault PatternsSFP12Faulty Memory Release
+ References
[REF-657] "boost C++ Library Smart Pointers". <https://www.boost.org/doc/libs/1_38_0/libs/smart_ptr/smart_ptr.htm>. URL validated: 2023-04-07.
[REF-480] "Valgrind". <http://valgrind.org/>.
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2009-05-08
(CWE 1.4, 2009-05-27)
CWE Content TeamMITRE
+ Modifications
Modification DateModifierOrganization
2010-06-21CWE Content TeamMITRE
updated Description
2010-09-27CWE Content TeamMITRE
updated Relationships
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2012-05-11CWE Content TeamMITRE
updated Common_Consequences, Demonstrative_Examples, Relationships
2012-10-30CWE Content TeamMITRE
updated Potential_Mitigations
2014-02-18CWE Content TeamMITRE
updated Potential_Mitigations
2014-07-30CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2017-11-08CWE Content TeamMITRE
updated Relationships
2019-06-20CWE Content TeamMITRE
updated Relationships
2020-02-24CWE Content TeamMITRE
updated Relationships
2020-12-10CWE Content TeamMITRE
updated Relationships
2021-03-15CWE Content TeamMITRE
updated Maintenance_Notes
2023-01-31CWE Content TeamMITRE
updated Description
2023-04-27CWE Content TeamMITRE
updated Detection_Factors, References, Relationships
2023-06-29CWE Content TeamMITRE
updated Mapping_Notes
2023-10-26CWE Content TeamMITRE
updated Observed_Examples
Page Last Updated: February 29, 2024