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.
CWE-590 Variant Incomplete
Free of Memory not on the Heap
This vulnerability occurs when a program calls free() on a memory pointer that wasn't originally allocated using standard heap functions like malloc(), calloc(), or realloc().
Definition
What is CWE-590?
This vulnerability occurs when a program calls free() on a memory pointer that wasn't originally allocated using standard heap functions like malloc(), calloc(), or realloc().
Calling free() on an invalid pointer corrupts the program's internal memory management structures. This corruption typically leads to a crash, but it can also create opportunities for an attacker to manipulate the memory process. In some cases, an attacker can steer the free() operation to target controllable memory locations, potentially altering critical variables or even executing malicious code.
Detecting these 'invalid free' issues manually is challenging, as they often involve complex pointer tracking across codebases. While SAST tools can flag the pattern, Plexicus uses AI to analyze the data flow and suggest precise code fixes, transforming a tedious security hunt into an automated remediation step and saving significant developer time.
Real-world impact
Real-world CVEs caused by CWE-590
No public CVE references are linked to this CWE in MITRE's catalog yet.
How attackers exploit it
Step-by-step attacker path
- 1
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.
- 2
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.
- 3
Instead, if the programmer wanted to dynamically manage the memory, malloc() or calloc() should have been used.
- 4
Additionally, global variables could be passed to free() when they are pointers to dynamically allocated memory.
Vulnerable code example
Vulnerable C
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.
void foo(){
record_t bar[MAX_SIZE];
```
/* do something interesting with bar */*
...
free(bar);} Secure code example
Secure C
Instead, if the programmer wanted to dynamically manage the memory, malloc() or calloc() should have been used.
void foo(){
record_t *bar = (record_t*)malloc(MAX_SIZE*sizeof(record_t));
```
/* do something interesting with bar */*
...
free(bar);} 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-590
- 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.
- Testing Use a tool that dynamically detects memory management problems, such as valgrind.
Detection signals
How to detect CWE-590
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 searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
CWE-590
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Frequently asked questions What is CWE-590?
How serious is CWE-590?
What languages or platforms are affected by CWE-590?
How can I prevent CWE-590?
How does Plexicus detect and fix CWE-590?
Where can I learn more about CWE-590?
Frequently asked questions
What is CWE-590?
This vulnerability occurs when a program calls free() on a memory pointer that wasn't originally allocated using standard heap functions like malloc(), calloc(), or realloc().
How serious is CWE-590?
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-590?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent CWE-590?
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. 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.
How does Plexicus detect and fix CWE-590?
Plexicus's SAST engine matches the data-flow signature for CWE-590 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-590?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/590.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-590
CWE-762 Parent
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-123 Can precede
Write-what-where Condition
A write-what-where condition occurs when an attacker can control both the data written and the exact memory location where it's written,…
Resources
Further reading
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