Agent skill · security · yaklang
dangling-markup-injection
Dangling markup injection playbook. Use when HTML injection is possible but JavaScript execution is blocked (CSP, sanitizer strips event handlers, WAF blocks script tags) — exfiltrate CSRF tokens, session data, and page content by injecting unclosed HTML tags that capture subsequent page content.
Why this skill is useful
Provides detailed techniques for exploiting HTML injection vulnerabilities that are often overlooked, enhancing the AI's understanding of web security.
What it needs
About 7k tokens when loaded. Last updated 2026-06-16. 1,563 stars on the source repository.
What this skill does
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: 1. You have an HTML injection point (reflected or stored) 2. JavaScript execution is blocked: CSP blocks inline scripts and event handlers Sanitizer strips <script>, onerror, onload, etc. WAF blocks known XSS patterns 3. 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. The browser interprets everything from https://attacker.com/collect? until the next " as the URL. The hidden CSRF token and email value become part of the URL query string sent to attacker.com. --- 3. …
How to use it
Reference it in AdaL, Claude Code, Cursor or any coding agent — nothing to install:
@skills yaklang/dangling-markup-injection