CWE-763 Base Incomplete

Release of Invalid Pointer or Reference

This vulnerability occurs when a program tries to free a memory resource back to the system but uses an incorrect deallocation method or calls the correct method improperly.

Definition

What is CWE-763?

This vulnerability occurs when a program tries to free a memory resource back to the system but uses an incorrect deallocation method or calls the correct method improperly.
This issue typically arises from mismatched memory management functions. For example, memory allocated with one function (like `malloc`) is incorrectly freed using a non-compatible function from a different API (like `delete`), leading to heap corruption and instability. This mismatch, often called CWE-762, breaks the underlying memory manager's expectations. Even when using the correct function pair, developers can misuse them. A common mistake is calling the deallocation function with an invalid pointer—such as one that was already freed, points to stack memory, or was never allocated. This scenario, related to CWE-761, causes crashes or undefined behavior because the system cannot process the flawed release request.
Real-world impact

Real-world CVEs caused by CWE-763

  • CVE-2019-11930

    function "internally calls 'calloc' and returns a pointer at an index... inside the allocated buffer. This led to freeing invalid memory."

How attackers exploit it

Step-by-step attacker path

  1. 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.

  2. 2

    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.

  3. 3

    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.

  4. 4

    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.

  5. 5

    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.

Vulnerable code example

Vulnerable C

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.

Vulnerable C 
char **ap, *argv[10], *inputstring;
  for (ap = argv; (*ap = strsep(&inputstring, " \t")) != NULL;)
  		if (**ap != '\0')
  			if (++ap >= &argv[10])
  				break;
  /.../
  free(ap[4]);
Secure code example

Secure C++

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.

Secure C++ 
void foo(){
  		BarObj *ptr = new BarObj()
```
/* do some work with ptr here */* 
  		
  		...
  		
  		delete ptr;}
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist

How to prevent CWE-763

  • 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().
  • Implementation When programming in C++, consider using smart pointers provided by the boost library to help correctly and consistently manage memory.
  • Architecture and Design 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.
  • Architecture and Design Use a language that provides abstractions for memory allocation and deallocation.
  • Testing Use a tool that dynamically detects memory management problems, such as valgrind.
Detection signals

How to detect CWE-763

Fuzzing High

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.

Plexicus auto-fix

Plexicus auto-detects CWE-763 and opens a fix PR in under 60 seconds.

Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.

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Frequently asked questions

Frequently asked questions

What is CWE-763?

This vulnerability occurs when a program tries to free a memory resource back to the system but uses an incorrect deallocation method or calls the correct method improperly.

How serious is CWE-763?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-763?

MITRE lists the following affected platforms: C, C++.

How can I prevent CWE-763?

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

How does Plexicus detect and fix CWE-763?

Plexicus's SAST engine matches the data-flow signature for CWE-763 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-763?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/763.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-763

CWE-404 Parent

Improper Resource Shutdown or Release

This vulnerability occurs when a program fails to properly close or release a system resource—like a file handle, database connection, or…

CWE-1266 Sibling

Improper Scrubbing of Sensitive Data from Decommissioned Device

This vulnerability occurs when a system lacks a reliable method for administrators to permanently erase sensitive information before…

CWE-299 Sibling

Improper Check for Certificate Revocation

This vulnerability occurs when an application fails to properly verify whether a security certificate has been revoked, potentially…

CWE-401 Sibling

Missing Release of Memory after Effective Lifetime

This vulnerability occurs when a program allocates memory but fails to properly release it after it's no longer needed, causing a gradual…

CWE-459 Sibling

Incomplete Cleanup

This vulnerability occurs when an application fails to properly remove temporary files, data structures, or system resources after they…

CWE-761 Sibling

Free of Pointer not at Start of Buffer

This vulnerability occurs when a program incorrectly frees a memory pointer that no longer points to the beginning of the allocated heap…

CWE-762 Sibling

Mismatched Memory Management Routines

This vulnerability occurs when a program uses incompatible functions to allocate and free memory. For example, freeing memory with a…

CWE-772 Sibling

Missing Release of Resource after Effective Lifetime

This vulnerability occurs when a program fails to properly release a system resource—like memory, file handles, or network sockets—after…

CWE-775 Sibling

Missing Release of File Descriptor or Handle after Effective Lifetime

This vulnerability occurs when a program fails to properly close file descriptors or handles after they are no longer needed, leaving…

Resources

Further reading

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