detecting-null-pointer-dereference

name	detecting-null-pointer-dereference
description	Detects null pointer dereference vulnerabilities by identifying unchecked pointer usage and missing validation. Use when analyzing pointer operations, input validation, or investigating crash vulnerabilities.

Null Pointer Dereference Detection

Detection Workflow

1. Identify pointer dereferences: Find all pointer dereferences (*ptr, ptr->field), array accesses (ptr[index]), function calls with pointer parameters, pointer operations
2. Trace pointer sources: Use xrefs_to to trace pointers, find where pointers originate, identify pointer assignments, track pointer values
3. Check null validation: Verify null checks before dereference, assess check completeness, identify missing validation paths, check validation logic correctness
4. Assess impact: Can attacker control pointer value? Is dereference reachable? What's the crash potential? Can it lead to security issues?

Key Patterns

• Missing null checks: pointer dereference without null check, function calls with unchecked pointers, array access through null pointers, member access through null pointers
• Conditional dereference: dereference after partial null check, dereference in only some code paths, dereference after pointer assignment, dereference in loop conditions
• Function parameter issues: unchecked function parameters, assumptions about non-null parameters, missing validation in public APIs, null pointers from external sources
• Return value issues: dereferencing potentially null return values, assuming malloc/new never returns null, missing checks on function returns, dereferencing failed allocations

Output Format

Report with: id, type, subtype, severity, confidence, location, dereferenced_pointer, dereference_type, dereference_operation, pointer_source, null_check, vulnerability, exploitable, attack_scenario, impact, mitigation.

Severity Guidelines

• HIGH: Null dereference in critical code paths
• MEDIUM: Null dereference causing crashes
• LOW: Null dereference with limited impact

See Also

• patterns.md - Detailed detection patterns and exploitation scenarios
• examples.md - Example analysis cases and code samples
• references.md - CWE references and mitigation strategies