MITRE’s description of CWE-122: A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
Common consequences MITRE lists
- Availability: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory)
- Integrity, Confidentiality, Availability, Access Control: Execute Unauthorized Code or Commands; Bypass Protection Mechanism; Modify Memory
- Integrity, Confidentiality, Availability, Access Control, Other: Execute Unauthorized Code or Commands; Bypass Protection Mechanism; Other
Overwriting heap memory corrupts allocator metadata and neighboring objects, which attackers can shape into code execution.
- Validate sizes before allocating and copying, including overflow in size calculations.
- Prefer memory-safe languages and containers that track their capacity.
- Use a hardened allocator and fuzz with AddressSanitizer.
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.
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-122 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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