MITRE’s description of CWE-476: The product dereferences a pointer that it expects to be valid but is NULL.
Common consequences MITRE lists
- Availability: DoS: Crash, Exit, or Restart
- Integrity, Confidentiality: Execute Unauthorized Code or Commands; Read Memory; Modify Memory
Dereferencing a null pointer usually crashes the process, giving attackers a reliable denial of service; in kernels and firmware it can sometimes be taken further.
- Check the results of allocation, lookup and parsing functions before using them.
- Use language features that make absence explicit, such as optional types and non-nullable references, and turn on the compiler’s null-safety warnings.
- Fuzz error paths and use static analysis that tracks nullability.
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.
Handle failures without leaking internals or weakening controls
Give callers a useful, bounded response while preserving protected diagnostic evidence and safe application state.
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-476 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.
CWE content: Copyright © 2006–2026, The MITRE Corporation. CWE, CWSS, CWRAF, and the CWE logo are trademarks of The MITRE Corporation. CWE™ is free to use by any organization or individual for any research, development, and/or commercial purposes, per these CWE Terms of Use. Accordingly, The MITRE Corporation hereby grants you a non-exclusive, royalty-free license to use CWE for research, development, and commercial purposes. Any copy you make for such purposes is authorized on the condition that you reproduce MITRE’s copyright designation and this license in any such copy. CWE is a trademark of The MITRE Corporation. CWE Terms of Use.