Individual skill
testing-for-crlf-injection
Testing web applications for CRLF (Carriage Return / Line Feed) injection where unsanitized %0d%0a sequences in user input let an attacker inject HTTP headers, split responses, poison caches, plant cookies, or pivot to XSS and request smuggling. Activates when user input is reflected into response headers, Location redirects, log files, or outbound requests made by the application.
internal/tools/skills/data/web-application-security/testing-for-crlf-injection/SKILL.md
Source commit d42f381ad34843e71a42658e5c57290c713e85af
What was checked
- Matches the observed repository HEAD
- Yes
- Scanner rules are current
- Yes
- Repository scan complete
- No
- Skill scan complete
- No
- Observed behavior
- Network or broad shell
- Last checked
- Nov 9, 2026
These are observations at the recorded commit, not a guarantee of safety. Review the source before running it.
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Repository context
- Repository stars (not skill ratings)
- 1,315
- Repository last updated
- Nov 8, 2026
- License
- Apache-2.0
Observed agent integration: No specific integration evidence. Standard SKILL.md installation does not imply verified compatibility.
- cybersecurity Repository topic
- security Repository topic
- bug-bounty Repository topic
- automation Repository topic
- autonomous-pentesting Repository topic
- ai-agent Repository topic
- ai-security Repository topic
- ethical-hacking Repository topic
- golang Repository topic
- penetration-testing Repository topic
- penetration-testing Declared skill tag
- crlf-injection Declared skill tag
- http-header-injection Declared skill tag
- response-splitting Declared skill tag
- owasp Declared skill tag
- web-security Declared skill tag
- security Derived category
- testing Derived category
- security-application Derived category
Files and excerpt
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# Testing for CRLF / HTTP Header Injection
## When to Use
- When user input is reflected into a response header (`Set-Cookie`, `Location`, `X-*`, custom headers)
- When testing redirect parameters (`?url=`, `?next=`, `?redirect=`) that feed a `Location:` header
- When the app writes user data into log files, session files, or memcache keys without sanitizing `\r\n`
- When an internal HTTP client (PHP `SoapClient`, RestSharp, Refit, Go/Java HTTP libs) builds requests from user input — header injection there enables SSRF / request smuggling
- When pre-auth session state is persisted to disk and later reloaded (newline injection can become an auth bypass)
## Critical: Variants Most Often Missed
Scanners stop after the literal `%0d%0a` is filtered. Carriage Return is `%0d` (`\r`), Line Feed is `%0a` (`\n`). For EVERY reflected/redirect/log parameter, run the full matrix:
