Web Application Security

CRLFuzz – A Fast Tool To Scan CRLF Vulnerability Written In Go

CRLFuzz - A Fast Tool To Scan CRLF Vulnerability Written In Go

[sc name=”ad_1″]

A fast tool to scan CRLF vulnerability written in Go


from Binary

The installation is easy. You can download a prebuilt binary from releases page, unpack and run! or with

$ curl -sSfL http://git.io/get-crlfuzz | sh -s -- -b /usr/local/bin

from Source

If you have go1.13+ compiler installed and configured:

$ GO111MODULE=on go get -v github.com/dwisiswant0/crlfuzz/cmd/crlfuzz

In order to update the tool, you can use -u flag with go get command.

from GitHub

$ git clone https://github.com/dwisiswant0/crlfuzz
$ cd crlfuzz/cmd/crlfuzz
$ go build .
$ mv crlfuzz /usr/local/bin


Basic Usage

Simply, CRLFuzz can be run with:

$ crlfuzz -u "http://target"


$ crlfuzz -h

This will display help for the tool. Here are all the switches it supports.

Flag Description
-u, –url Define single URL to fuzz
-l, –list Fuzz URLs within file
-X, –method Specify request method to use (default: GET)
-o, –output File to save results
-d, –data Define request data
-H, –header Pass custom header to target
-x, –proxy Use specified proxy to fuzz
-c, –concurrent Set the concurrency level (default: 25)
-s, –silent Silent mode
-v, –verbose Verbose mode
-V, –version Show current CRLFuzz version
-h, –help Display its help


You can define a target in 3 ways:

Single URL

$ crlfuzz -u "http://target"

URLs from list

$ crlfuzz -l /path/to/urls.txt

from Stdin

In case you want to chained with other tools.

$ subfinder -d target -silent | httpx -silent | crlfuzz


By default, CRLFuzz makes requests with GET method. If you want to change it, you can use the -X flag.

$ crlfuzz -u "http://target" -X "GET"


You can also save fuzzing results to a file with -o flag.

$ crlfuzz -l /path/to/urls.txt -o /path/to/results.txt


If you want to send a data request using POST, DELETE. PATCH or other methods, you just need to use -d flag.

$ crlfuzz -u "http://target" -X "POST" -d "data=body"

Adding Headers

May you want to use custom headers to add cookies or other header parts.

$ crlfuzz -u "http://target" -H "Cookie: ..." -H "User-Agent: ..."

Using Proxy

Using a proxy, proxy string can be specified with a protocol:// prefix to specify alternative proxy protocols.

$ crlfuzz -u "http://target" -x


Concurrency is the number of fuzzing at the same time. Default value CRLFuzz provide is 25, you can change it by using -c flag.

$ crlfuzz -l /path/to/urls.txt -c 50


If you activate this silent mode with the -s flag, you will only see vulnerable targets.

$ crlfuzz -l /path/to/urls.txt -s | tee vuln-urls.txt


Unlike silent mode, it will display error details if there is an error with the -v flag.

$ crlfuzz -l /path/to/urls.txt -v


To display the current version of CRLFuzz with the -V flag.

$ crlfuzz -V


You can use CRLFuzz as a library.

package main
import (
func main() {
target := "http://target"
method := "GET"
// Generates a potentially CRLF vulnerable URLs
for _, url := range crlfuzz.GenerateURL(target) {
// Scan against target
vuln, err := crlfuzz.Scan(url, method, "", []string{}, "")
if err != nil {
if vuln {
fmt.Printf("VULN! %sn", url)

Help & Bugs

If you are still confused or found a bug, please open the issue. All bug reports are appreciated, some features have not been tested yet due to lack of free time.


CRLFuzz released under MIT. See LICENSE for more details.


Current version is 1.3.0 and still development.

[sc name=”ad-in-article”]