# Detecting Arbitrary Write > Detects arbitrary write vulnerabilities by identifying unchecked array indexing and out-of-bounds memory writes. Use when analyzing memory write operations, pointer arithmetic, or investigating code execution vulnerabilities. Use when this capability is needed. - Skill: `tomevault-io/detecting-arbitrary-write` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/detecting-arbitrary-write` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/detecting-arbitrary-write/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/detecting-arbitrary-write --- # Arbitrary Write Detection ## Detection Workflow 1. **Identify write operations**: Find all array writes, pointer dereference writes, format string usage with %n, struct member writes 2. **Trace input sources**: Use `xrefs_to` to trace input, follow user data to write points, identify attacker-controlled values 3. **Check bounds validation**: Verify array bounds checks, assess pointer arithmetic safety, check format string validation, review type safety 4. **Assess exploitability**: Can attacker control write address? Can attacker control write value? What can be overwritten? Can code execution be achieved? ## Key Patterns - Unchecked array indexing: array writes with user-controlled indices, pointer arithmetic writes with user input - Format string writes: user-controlled format strings with %n, memory writes via printf - Pointer dereference writes: writing through user-controlled pointers, use-after-free writes, vtable corruption - Struct/class member writes: writing to wrong struct members, type confusion, vtable/function pointer overwrites ## Output Format Report with: id, type, subtype, severity, confidence, location, vulnerability, write operation, array base, index source, value source, bounds check, exploitable, attack scenario, potential targets, mitigation. ## Severity Guidelines - **CRITICAL**: Arbitrary write enabling code execution - **HIGH**: Arbitrary write with significant impact - **MEDIUM**: Arbitrary write with limited impact - **LOW**: Minor arbitrary write issues ## 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 --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/waiwai24) — claim your Tome and manage your conversions.