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Smuggler – An HTTP Request Smuggling / Desync Testing Tool

An HTTP Request Smuggling / Desync testing tool written in Python 3


A special thanks to James Kettle for his research and methods into HTTP desyncs

And a special thanks to Ben Sadeghipour for beta testing Smuggler and for allowing me to discuss my work at Nahamcon 2020


This tool does not guarantee no false-positives or false-negatives. Just because a mutation may report OK does not mean there isn’t a desync issue, but more importantly just because the tool indicates a potential desync issue does not mean there definitely exists one. The script may encounter request processors from large entities (i.e. Google/AWS/Yahoo/Akamai/etc..) that may show false positive results.


  1. git clone
  2. cd smuggler
  3. python3 -h

Example Usage

Single Host:

<div class="snippet-clipboard-content position-relative overflow-auto" data-snippet-clipboard-copy-content="python3 -u “>

python3 -u <URL>

List of hosts:

cat list_of_hosts.txt | python3


usage: [-h] [-u URL] [-v VHOST] [-x] [-m METHOD] [-l LOG] [-q]
[-t TIMEOUT] [--no-color] [-c CONFIGFILE]

optional arguments:
-h, --help show this help message and exit
-u URL, --url URL Target URL with Endpoint
-v VHOST, --vhost VHOST
Specify a virtual host
-x, --exit_early Exit scan on first finding
-m METHOD, --method METHOD
HTTP method to use (e.g GET, POST) Default: POST
-l LOG, --log LOG Specify a log file
-q, --quiet Quiet mode will only log issues found
-t TIMEOUT, --timeout TIMEOUT
Socket timeout value Default: 5
--no-color Suppress color codes
Filepath to the configuration file of payloads

Smuggler at a minimum requires either a URL via the -u/–url argument or a list of URLs piped into the script via stdin. If the URL specifies https:// then Smuggler will connect to the host:port using SSL/TLS. If the URL specifies http:// then no SSL/TLS will be used at all. If only the host is specified, then the script will default to https://

Use -v/–vhost <host> to specify a different host header from the server address

Use -x/–exit_early to exit the scan of a given server when a potential issue is found. In piped mode smuggler will just continue to the next host on the list

Use -m/–method <method> to specify a different HTTP verb from POST (i.e GET/PUT/PATCH/OPTIONS/CONNECT/TRACE/DELETE/HEAD/etc…)

Use -l/–log <file> to write output to file as well as stdout

Use -q/–quiet reduce verbosity and only log issues found

Use -t/–timeout <value> to specify the socket timeout. The value should be high enough to conclude that the socket is hanging, but low enough to speed up testing (default: 5)

Use –no-color to suppress the output color codes printed to stdout (logs by default don’t include color codes)

Use -c/–configfile <configfile> to specify your smuggler mutation configuration file (default:

Config Files

Configuration files are python files that exist in the ./config directory of smuggler. These files describe the content of the HTTP requests and the transfer-encoding mutations to test.

Here is example content of

def render_template(gadget):
RN = "\r\n"
p = Payload()
p.header = "__METHOD__ __ENDPOINT__?cb=__RANDOM__ HTTP/1.1" + RN
# p.header += "Transfer-Encoding: chunked" +RN
p.header += gadget + RN
p.header += "Host: __HOST__" + RN
p.header += "User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.87 Safari/537.36" + RN
p.header += "Content-type: application/x-www-form-urlencoded; charset=UTF-8" + RN
p.header += "Content-Length: __REPLACE_CL__" + RN
return p

mutations["nameprefix1"] = render_template(" Transfer-Encoding: chunked")
mutations["tabprefix1"] = render_template("Transfer-Encoding:\tchunked")
mutations["tabprefix2"] = render_template("Transfer-Encoding\t:\tchunked")
mutations["space1"] = render_template("Transfer-Encoding : chunked")

for i in [0x1,0x4,0x8,0x9,0xa,0xb,0xc,0xd,0x1F,0x20,0x7f,0xA0,0xFF]:
mutations["midspace-% 02x"%i] = render_template("Transfer-Encoding:%cchunked"%(i))
mutations["postspace-%02x"%i] = render_template("Transfer-Encoding%c: chunked"%(i))
mutations["prespace-%02x"%i] = render_template("%cTransfer-Encoding: chunked"%(i))
mutations["endspace-%02x"%i] = render_template("Transfer-Encoding: chunked%c"%(i))
mutations["xprespace-%02x"%i] = render_template("X: X%cTransfer-Encoding: chunked"%(i))
mutations["endspacex-%02x"%i] = render_template("Transfer-Encoding: chunked%cX: X"%(i))
mutations["rxprespace-%02x"%i] = render_template("X: X\r%cTransfer-Encoding: chunked"%(i))
mutations["xnprespace-%02x"%i] = render_template("X: X%c\nTransfer-Encoding: chunked"%(i))
mutations["endspacerx-%02x"%i] = render_template("Transfer-Encoding: chunked\r%cX: X"%(i))
mutations["endspacexn-%02x"%i] = render_template("Transfer-Encoding: chunked%c\nX: X"%(i))

There are no input arguments yet on specifying your own customer headers and user-agents. It is recommended to create your own configuration file based on and modify it to your liking.

Smuggler comes with 3 configuration files: (fast), (niche, slow), (very slow) is the fastest because it contains less mutations.

specify configuration files using the -c/–configfile <configfile> command line option

Payloads Directory

Inside the Smuggler directory is the payloads directory. When Smuggler finds a potential CLTE or TECL desync issue, it will automatically dump a binary txt file of the problematic payload in the payloads directory. All payload filenames are annotated with the hostname, desync type and mutation type. Use these payloads to netcat directly to the server or to import into other analysis tools.

Helper Scripts

After you find a desync issue feel free to use my Turbo Intruder desync scripts found Here: and are great scripts to help stage a desync attack


These scripts are released under the MIT license. See LICENSE.

Source : KitPloit – PenTest Tools!

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