MITRE’s description of CWE-416: The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
Common consequences MITRE lists
- Integrity: Modify Memory
- Availability: DoS: Crash, Exit, or Restart
- Confidentiality: Read Memory
- Integrity, Confidentiality, Availability: Execute Unauthorized Code or Commands
Once freed memory is reused, the stale pointer reads or writes whatever now lives there; attackers shape that memory to leak data or take control of execution.
- Prefer memory-safe languages, or ownership types such as
std::unique_ptrin C++, so that object lifetimes are enforced. - Clear pointers after freeing them and do not keep raw pointers across callbacks, threads or asynchronous work.
- Test with AddressSanitizer and fuzzing, and use a hardened allocator where the platform offers one.
Guides on this site
Find, fix and contain memory-safety bugs in C and C++
Recognize out-of-bounds access, use after free, NULL dereference and integer overflow in C and C++, fix them with checked lengths and single ownership, harden release builds, catch the rest with sanitizers and fuzzing, and plan new code in a memory-safe language.
Audit unsafe Rust, FFI boundaries and crate dependencies
Know what the Rust compiler proves and what it leaves to you: review unsafe code for soundness, wrap foreign calls in small safe functions, decide how overflow and panics behave in release builds, gate crates with RustSec, and replace C one boundary at a time.
Fuzz a parser and turn crashes into lasting regressions
Build a narrow harness, observe memory and resource failures, minimize the input, and test the repaired parser.
Practice
- Buffer over-read lab: Stop a heartbeat over-read · Browser lab
- Parse bounded JSON and XML invoices safely · Local project
- Repair a native parser using sanitizer evidence · Local project
References
- CWE-416 in the MITRE CWE list (version 4.20)
- 2025 CWE Top 25 Most Dangerous Software Weaknesses (MITRE CWE Program)
List data from MITRE; the name, definition and consequences are from MITRE’s CWE 4.20 catalogue. A guide is listed as the main subject when the weakness is what the guide is about, and as covering it when a dedicated section or worked example addresses it.
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