CWE-590: Free of Memory not on the Heap

Description

The product calls free() on a pointer to memory that was not allocated using associated heap allocation functions such as malloc(), calloc(), or realloc().

When free() is called on an invalid pointer, the program's memory management data structures may become corrupted. This corruption can cause the program to crash or, in some circumstances, an attacker may be able to cause free() to operate on controllable memory locations to modify critical program variables or execute code.

Potential Impact

Integrity, Confidentiality, Availability

Execute Unauthorized Code or Commands, Modify Memory

Demonstrative Examples

In this example, an array of record_t structs, bar, is allocated automatically on the stack as a local variable and the programmer attempts to call free() on the array. The consequences will vary based on the implementation of free(), but it will not succeed in deallocating the memory.

Bad

void foo(){
                        record_t bar[MAX_SIZE];
                           
                           /* do something interesting with bar */
                           
                           ...free(bar);
                     }

This example shows the array allocated globally, as part of the data segment of memory and the programmer attempts to call free() on the array.

Bad

record_t bar[MAX_SIZE]; //Global varvoid foo(){
                        
                           
                           /* do something interesting with bar */
                           ...free(bar);
                     }

Instead, if the programmer wanted to dynamically manage the memory, malloc() or calloc() should have been used.

Good

void foo(){
                        record_t *bar = (record_t*)malloc(MAX_SIZE*sizeof(record_t));
                           
                           /* do something interesting with bar */
                           
                           ...free(bar);
                     }

Additionally, global variables could be passed to free() when they are pointers to dynamically allocated memory.

Good

record_t *bar; //Global varvoid foo(){
                        bar = (record_t*)malloc(MAX_SIZE*sizeof(record_t));
                           
                           /* do something interesting with bar */
                           
                           ...free(bar);
                     }

Mitigations & Prevention

Implementation

Only free pointers that you have called malloc on previously. This is the recommended solution. Keep track of which pointers point at the beginning of valid chunks and free them only once.

Implementation

Before freeing a pointer, the programmer should make sure that the pointer was previously allocated on the heap and that the memory belongs to the programmer. Freeing an unallocated pointer will cause undefined behavior in the program.

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.

Detection Methods

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,
Automated Static Analysis High — Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then sea
Automated Dynamic Analysis Moderate — Use tools that are integrated during compilation to insert runtime error-checking mechanisms related to memory safety errors, such as AddressSanitizer (ASan) for C/C++ [REF-1518] or valgrind [REF-480].

Real-World CVE Examples

CVE ID	Description
CVE-2023-22291	parser for a word processor attempts to free a stack pointer when intending to expand memory to hold a larger buffer

Taxonomy Mappings

CERT C Secure Coding: MEM34-C — Only free memory allocated dynamically
CERT C Secure Coding: WIN30-C — Properly pair allocation and deallocation functions
Software Fault Patterns: SFP12 — Faulty Memory Release

Frequently Asked Questions

What is CWE-590?

CWE-590 (Free of Memory not on the Heap) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. The product calls free() on a pointer to memory that was not allocated using associated heap allocation functions such as malloc(), calloc(), or realloc().

How can CWE-590 be exploited?

Attackers can exploit CWE-590 (Free of Memory not on the Heap) to execute unauthorized code or commands, modify memory. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-590?

Key mitigations include: Only free pointers that you have called malloc on previously. This is the recommended solution. Keep track of which pointers point at the beginning of valid chunks and free them only once.

What is the severity of CWE-590?

CWE-590 is classified as a Variant-level weakness (Low-Medium abstraction). It has been observed in 1 real-world CVEs.