HackSkills is an organized knowledge base of installable skills that gives AI agents practical security knowledge across areas such as web security, privilege escalation, reverse engineering, and digital forensics. It is intended for bug bounty work, penetration testing, CTF competitions, and authorized security research. The catalogue entries are the project's own master, category, and topic skills.
Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/yaklang/hack-skills/vm-and-bytecode-reversenpx skills add yaklang/hack-skills --skill vm-and-bytecode-reversegit clone --depth 1 https://github.com/yaklang/hack-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/yaklang/hack-skills/vm-and-bytecode-reverse)<a href="https://agentmods.dev/skills/yaklang/hack-skills/vm-and-bytecode-reverse"><img src="https://agentmods.dev/badge/skills/yaklang/hack-skills/vm-and-bytecode-reverse.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00042 | $0.04195 |
| Opus 5 | $0.00021 | $0.02098 |
| Sonnet 5 | $0.00008 | $0.00839 |
| Haiku 4.5 | $0.00004 | $0.00419 |
Grade A, and why
vm-and-bytecode-reverse scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
Copies of this mod
3 near-identical copies found in the catalogue:
- vm-and-bytecode-reverse — 100% identical, 0 lines differ
- vm-and-bytecode-reverse — 100% identical, 0 lines differ
- vm-and-bytecode-reverse — 94% identical, 6 lines differ
How it starts
The opening of the file, as written. The whole thing — 451 lines — stays where its author put it; the contents beside it link to each section on GitHub.
SKILL: VM & Bytecode Reverse Engineering — Expert Analysis Playbook
AI LOAD INSTRUCTION: Expert techniques for reversing custom virtual machines and bytecode interpreters. Covers dispatcher identification, opcode mapping, custom ISA reconstruction, disassembler/decompiler writing, maze challenges, and real-world VM protector analysis. Base models often fail to recognize the fetch-decode-execute pattern or attempt to analyze VM bytecode as native code.
0. RELATED ROUTING
- code-obfuscation-deobfuscation when the VM is a commercial protector (VMProtect/Themida)
- symbolic-execution-tools when using angr to solve VM-based challenges
- anti-debugging-techniques when the VM includes anti-debug checks
Quick identification
| Binary Pattern | Likely VM Type | Start With |
|---|---|---|
while(1) { switch(bytecode[pc]) } |
Switch-based dispatcher | Map each case to an operation |
Indirect jump via table jmp [table + opcode*8] |
Table-based dispatcher | Dump jump table, analyze handlers |
| Nested if-else chain on byte value | If-chain dispatcher | Same as switch, just different syntax |
| Stack push/pop dominant operations | Stack-based VM | Identify push, pop, arithmetic ops |
reg[X] = ... array operations |
Register-based VM | Map register indices to operations |
| 2D grid + direction input | Maze challenge | Extract grid, apply BFS/DFS |
1. CUSTOM VM IDENTIFICATION
1.1 Structural Indicators
VM Architecture Components:
┌─────────────────────────────────┐
│ Bytecode Program (data section)│
├─────────────────────────────────┤
│ Program Counter (pc/ip) │
│ Register File / Stack │
│ Memory / Data Area │
├─────────────────────────────────┤
│ Dispatcher Loop │
│ ├─ Fetch: opcode = code[pc] │
│ ├─ Decode: lookup handler │
│ └─ Execute: run handler │
└─────────────────────────────────┘
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 2d ago First seen · 451 lines · 42 tokens per session scan A 4da387769cea
vm-and-bytecode-reverse is a skill published in the GitHub repository yaklang/hack-skills (2,098 stars, last pushed 2mo ago), licensed MIT. It adds 42 tokens to every session and 4,195 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
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