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name: detecting-off-by-one description: Detects off-by-one errors by identifying incorrect loop conditions, array indexing mistakes, and boundary condition problems. Use when analyzing loops, array access, or investigating fencepost errors.

Off-by-One Detection

Detection Workflow

1. Identify array operations: Find all array accesses, loop iterations, buffer allocations, string operations
2. Analyze boundary conditions: Check loop termination conditions, array index ranges, buffer size calculations
3. Check edge cases: Test boundary conditions, verify fencepost cases, assess null terminator handling
4. Assess impact: Can off-by-one cause overflow/underflow? What's the security impact?

Key Patterns

• Loop bound errors: using <= instead of <, or < instead of <=
• Array index errors: accessing array[size] instead of array[size-1]
• String handling errors: missing null terminator, incorrect buffer size
• Allocation errors: allocating size instead of size+1

Output Format

Report with: id, type, subtype, severity, confidence, location, vulnerability, loop condition, array access, array size, error type, exploitability, attack scenario, impact, mitigation.

Severity Guidelines

• HIGH: Off-by-one causing buffer overflow
• MEDIUM: Off-by-one causing information disclosure
• LOW: Off-by-one with minor 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