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-415 Variant Draft
Double Free
A double free vulnerability occurs when a program mistakenly calls the 'free()' function twice on the same block of memory.
Definition
What is CWE-415?
A double free vulnerability occurs when a program mistakenly calls the 'free()' function twice on the same block of memory.
This happens when a developer loses track of which pointers reference already-freed memory. The first free() call returns the memory to the system's pool for reuse, but the second call targets the same now-invalid address. This corrupts the memory manager's internal data structures, which can immediately crash the program or, more dangerously, create an opening for attackers to execute arbitrary code.
Preventing double frees requires disciplined pointer management, such as setting pointers to NULL immediately after freeing them. While SAST tools can catch this pattern, Plexicus uses AI to suggest the actual code fix—like inserting that null assignment—saving hours of manual review and helping to secure your application's memory handling.
Real-world impact
Real-world CVEs caused by CWE-415
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Chain: Signal handler contains too much functionality (CWE-828), introducing a race condition (CWE-362) that leads to a double free (CWE-415).
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Double free resultant from certain error conditions.
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Double free resultant from certain error conditions.
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Double free resultant from certain error conditions.
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Double free from invalid ASN.1 encoding.
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Double free from malformed GIF.
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Double free from malformed GIF.
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Double free from malformed compressed data.
How attackers exploit it
Step-by-step attacker path
- 1
The following code shows a simple example of a double free vulnerability.
- 2
Double free vulnerabilities have two common (and sometimes overlapping) causes:
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- Error conditions and other exceptional circumstances - Confusion over which part of the program is responsible for freeing the memory
- 4
Although some double free vulnerabilities are not much more complicated than this example, most are spread out across hundreds of lines of code or even different files. Programmers seem particularly susceptible to freeing global variables more than once.
- 5
While contrived, this code should be exploitable on Linux distributions that do not ship with heap-chunk check summing turned on.
Vulnerable code example
Vulnerable C
The following code shows a simple example of a double free vulnerability.
char* ptr = (char*)malloc (SIZE);
...
if (abrt) {
free(ptr);
}
...
free(ptr); Secure code example
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} 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-415
- Architecture and Design Choose a language that provides automatic memory management.
- Implementation Ensure that each allocation is freed only once. After freeing a chunk, set the pointer to NULL to ensure the pointer cannot be freed again. In complicated error conditions, be sure that clean-up routines respect the state of allocation properly. If the language is object oriented, ensure that object destructors delete each chunk of memory only once.
- Implementation Use a static analysis tool to find double free instances.
Detection signals
How to detect CWE-415
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-415
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-415?
How serious is CWE-415?
What languages or platforms are affected by CWE-415?
How can I prevent CWE-415?
How does Plexicus detect and fix CWE-415?
Where can I learn more about CWE-415?
Frequently asked questions
What is CWE-415?
A double free vulnerability occurs when a program mistakenly calls the 'free()' function twice on the same block of memory.
How serious is CWE-415?
MITRE rates the likelihood of exploit as High — this weakness is actively exploited in the wild and should be prioritized for remediation.
What languages or platforms are affected by CWE-415?
MITRE lists the following affected platforms: C, C++.
How can I prevent CWE-415?
Choose a language that provides automatic memory management. Ensure that each allocation is freed only once. After freeing a chunk, set the pointer to NULL to ensure the pointer cannot be freed again. In complicated error conditions, be sure that clean-up routines respect the state of allocation properly. If the language is object oriented, ensure that object destructors delete each chunk of memory only once.
How does Plexicus detect and fix CWE-415?
Plexicus's SAST engine matches the data-flow signature for CWE-415 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-415?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/415.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-415
CWE-825 Parent
Expired Pointer Dereference
This vulnerability occurs when a program tries to use a pointer that still points to a memory location that has already been freed or…
CWE-416 Sibling
Use After Free
Use After Free happens when a program continues to use a pointer to a memory location after that memory has been freed. This can lead to…
CWE-123 Peer
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,…
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