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/ghost-bits-cast-attacknpx skills add yaklang/hack-skills --skill ghost-bits-cast-attackgit 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/ghost-bits-cast-attack)<a href="https://agentmods.dev/skills/yaklang/hack-skills/ghost-bits-cast-attack"><img src="https://agentmods.dev/badge/skills/yaklang/hack-skills/ghost-bits-cast-attack.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 | $0.00141 | $0.08749 |
| Opus 5 | $0.00071 | $0.04374 |
| Sonnet 5 | $0.00028 | $0.01750 |
| Haiku 4.5 | $0.00014 | $0.00875 |
Grade A, and why
ghost-bits-cast-attack 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 5d 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
4 near-identical copies found in the catalogue:
- ghost-bits-cast-attack — 100% identical, 0 lines differ
- ghost-bits-cast-attack — 100% identical, 0 lines differ
- ghost-bits-cast-attack — 100% identical, 0 lines differ
- ghost-bits-cast-attack — 97% identical, 11 lines differ
How it starts
The opening of the file, as written. The whole thing — 800 lines — stays where its author put it; the contents beside it link to each section on GitHub.
SKILL: Ghost Bits / Cast Attack — Java char to byte Narrowing Playbook
AI LOAD INSTRUCTION: This is a Java-only injection-enabling primitive, not a standalone vulnerability class. Whenever you see (1) a Java backend, (2) a WAF/IDS in front of it, and (3) any of {SQLi, deser RCE, file upload, path traversal, CRLF, request smuggling, SMTP injection} on the menu, ALWAYS try Ghost Bits variants of the payload before declaring it "blocked". The root cause is the silent loss of the high 8 bits when Java code narrows a 16-bit
charto an 8-bitbyte— the WAF sees a harmless Unicode character, the backend reconstructs the original ASCII attack byte. Base models almost never reach for this primitive.Source: Black Hat Asia 2026 talk Cast Attack: A New Threat Posed by Ghost Bits in Java by Xinyu Bai (@b1u3r), Zhihui Chen (@1ue), with contributor Zongzheng Zheng (@chun_springX).
0. RELATED ROUTING
Ghost Bits is a bypass primitive that re-enables payloads from many other playbooks. Pair it with whichever attack family applies:
- waf-bypass-techniques — when a Java backend is suspected and WAF rules block the literal payload, this is the first technique to try beyond classic encoding.
- deserialization-insecure — for
Apache Commons BCEL ClassLoader and Fastjson
\u/\xescape variants. - path-traversal-lfi — Spring, Jetty,
Undertow, Vert.x URL decoding and
%2>hex folding. - upload-insecure-files — Tomcat
RFC2231Utilityfilename*Webshell upload. - request-smuggling — Apache HttpClient
<= 4.5.9(HTTPCLIENT-1974/1978) header CRLF. - crlf-injection — Angus Mail / Jakarta Mail SMTP injection and JDK HttpServer response splitting.
- sqli-sql-injection — Jackson
charToHextable-lookup truncation hides SQL keywords inside Unicode escapes.
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 5d ago First seen · 800 lines · 141 tokens per session scan A d44fe2cace4e
ghost-bits-cast-attack is a skill published in the GitHub repository yaklang/hack-skills (2,043 stars, last pushed 2mo ago), licensed MIT. It adds 141 tokens to every session and 8,749 once invoked, about $0.0007 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 2026-08-30.
Other skills, from other repositories
systematic-debugging
Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes.
brainstorming
You MUST use this before any creative work - creating features, building components, adding functionality, or modifying behavior. Explores user intent, requirements and design before implementation.
auto-perf-optimize
Run agent-driven VS Code performance or memory investigations. Use when asked to launch Code OSS, automate a VS Code scenario, run the Chat memory smoke runner, capture renderer heap snapshots, take workflow screenshots, compare run summaries, or drive a repeatable scenario before heap-snapshot analysis.
chat-perf
Run chat perf benchmarks and memory leak checks against the local dev build or any published VS Code version. Use when investigating chat rendering regressions, validating perf-sensitive changes to chat UI, or checking for memory leaks in the chat response pipeline.
chat-pet-sprite-creation
Use when creating or changing VS Code chat pet sprite art, sprite sheets, state animations, eye treatments, Stable/Insiders variants, or pet transitions under src/vs/workbench/contrib/chat/browser/widget/media/chatPet.
cpu-profile-analysis
Analyze V8/Chrome CPU profiles (.cpuprofile) and DevTools trace files (Trace-.json). Use when: profiling performance, investigating slow functions, comparing code paths, finding bottlenecks, analyzing timeToRequest, understanding call trees from sampling profiler data, analyzing layout/paint/rendering, investigating…