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 skills add yaklang/hack-skills --skill dangling-markup-injectiongit 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/dangling-markup-injection)<a href="https://agentmods.dev/skills/yaklang/hack-skills/dangling-markup-injection"><img src="https://agentmods.dev/badge/skills/yaklang/hack-skills/dangling-markup-injection.svg" alt="Measured on agentmods" height="20"></a>- Socket fail
- Snyk fail
- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to high
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- high Prompt Injection · line 76 Hidden instructions were detected in comments or invisible text. These could contain malicious directives. Manual review is recommended.Fix: Audit all comments and invisible characters. Remove any instructions that direct the agent to perform unauthorized actions. Use plain, reviewable content.
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 | $0.00067 | $0.03325 |
| Opus 5 | $0.00034 | $0.01663 |
| Sonnet 5 | $0.00013 | $0.00665 |
| Haiku 4.5 | $0.00007 | $0.00332 |
Grade A, and why
dangling-markup-injection 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 8d 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:
- dangling-markup-injection — 100% identical, 0 lines differ
- dangling-markup-injection — 100% identical, 0 lines differ
- dangling-markup-injection — 100% identical, 0 lines differ
- dangling-markup-injection — 98% identical, 7 lines differ
How it starts
The opening of the file, as written. The whole thing — 322 lines — stays where its author put it; the contents beside it link to each section on GitHub.
SKILL: Dangling Markup Injection — Exfiltration Without JavaScript
AI LOAD INSTRUCTION: Covers dangling markup exfiltration via unclosed img/form/base/meta/link/table tags, what can be stolen (CSRF tokens, pre-filled form values, sensitive content), browser-specific behavior, and combinations with other attacks. Base models often overlook this technique entirely when CSP blocks scripts, jumping to "not exploitable" — dangling markup is the answer.
0. RELATED ROUTING
- xss-cross-site-scripting when full XSS is possible (no need for dangling markup)
- csp-bypass-advanced when CSP blocks JS execution — dangling markup bypasses script restrictions
- csrf-cross-site-request-forgery when dangling markup steals CSRF tokens for subsequent CSRF attacks
- crlf-injection when CRLF enables HTML injection in HTTP response
- web-cache-deception when dangling markup + cache poisoning amplifies the attack
1. WHEN TO USE DANGLING MARKUP
You need dangling markup when ALL of these are true:
- You have an HTML injection point (reflected or stored)
- JavaScript execution is blocked:
- CSP blocks inline scripts and event handlers
- Sanitizer strips
<script>,onerror,onload, etc. - WAF blocks known XSS patterns
- The page contains sensitive data AFTER your injection point:
- CSRF tokens
- Pre-filled form values (email, username, API keys)
- Session identifiers in hidden fields
- Sensitive user content
Core insight: You don't need JavaScript to exfiltrate data — you just need the browser to make a request that includes the data in the URL.
2. CORE TECHNIQUE
Inject an unclosed HTML tag with a src, href, action, or similar attribute pointing to your server. The unclosed attribute quote "consumes" all subsequent page content until the browser finds a matching quote.
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.
- 8d ago First seen · 322 lines · 67 tokens per session scan A 0fce78cc132d
dangling-markup-injection is a skill published in the GitHub repository yaklang/hack-skills (2,120 stars, last pushed 2mo ago), licensed MIT. It adds 67 tokens to every session and 3,325 once invoked, about $0.0003 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.
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