CRLF injection playbook. Use when user input reaches HTTP response headers, Location redirects, Set-Cookie values, or log files where carriage-return/line-feed characters can split or inject content.

SKILL: CRLF Injection — Expert Attack Playbook AI LOAD INSTRUCTION : CRLF injection (HTTP response splitting) techniques. Covers header injection, response body injection via double CRLF, XSS escalation, cache poisoning, and encoding bypass. Often overlooked by scanners but chains into XSS, session fixation, and cache attacks. 0. RELATED ROUTING [ghost bits cast attack](../ghost bits cast attack/SKILL.md) when the target is a Java service and %0D%0A / \r\n encodings are WAF blocked — substituting 瘍 (U+760D, low byte \r ) and 瘊 (U+760A, low byte \n ) injects a real CRLF through Angus Mail / Jakarta Mail SMTP, Apache HttpClient headers, JDK HttpServer responses, and ActiveJ HTTP (re enables Jira CVE 2025 57733 and JDK CVE 2026 21933 classes) 1. CORE CONCEPT CRLF = \r\n (Carriage Return + Line Feed, %0D%0A ). HTTP headers are separated by CRLF. If user input is reflected in a response header without sanitization, injecting CRLF characters creates new headers or even a response body. 2. DETECTION Basic Probe Double CRLF — Body Injection Two consecutive CRLF sequences end headers and start body: 3. EXPLOITATION SCENARIOS Session Fixation via Set Cookie XSS via Response Body Cache Poisoning If the response is cached by a CDN or proxy, injected headers/body are served to all users: Log Injection CRLF in log visible fields (User Agent, Referer) can forge log entries: 4. FILTER BYPASS Filter Bypass Blocks %0D%0A Try %0D alone, %0A alone, or %E5%98%8A%E5%98%8D (Unicode) URL decodes once Double encode: %250D%250A Strips \r\n literally Use URL encoded form Blocks in value only Inject in parameter name 5. REAL WORLD EXPLOITATION CHAINS CRLF + Session Fixation CRLF → XSS via Double CRLF Body Injection CRLF in 302 Location → Redirect Hijack 6. COMMON VULNERABLE PATTERNS 7. TESTING CHECKLIST

crlf-injection