Tags: web 

Rating: 0

# ▼▼▼Slash Slash(Web:50、174/696=25%)▼▼▼

This writeup is written by [**@kazkiti_ctf**](https://twitter.com/kazkiti_ctf)

```
//
Author: maskofmydisguise

handout_slashslash.7z

```

---

## 【Confirmation of attached file】

All source code was presented.

---

application.py

```
import os
from flask import Flask, render_template, jsonify

app = Flask(__name__)

'''
secret_key using python3 secrets module
'''
app.secret_key = "9d367b3ba8e8654c6433379763e80c6e"

'''
Learn about virtualenv here:
https://www.youtube.com/watch?v=N5vscPTWKOk&list=PL-osiE80TeTt66h8cVpmbayBKlMTuS55y&index=7
'''

FLAG = os.getenv("FLAG", "encryptCTF{}")

@app.route('/')
def index():
return render_template('index.html')

@app.route('/encryptCTF', methods=["GET"])
def getflag():
return jsonify({
'flag': FLAG
})

if __name__ == '__main__':
app.run(debug=False)
```

`FLAG = os.getenv("FLAG", "encryptCTF{}")`

It is obtained from **environment variable FLAG**.

---

## 【Way of thinking】

There is no need to build an environment and do a black box test.

It is better to look at the source code.

From now on, it searches for the file which sets the environment variable.

---

## 【searches for the file which sets the environment variable】

/app/env/bin/activate

```
# This file must be used with "source bin/activate" *from bash*
# you cannot run it directly

deactivate () {
unset -f pydoc >/dev/null 2>&1

# reset old environment variables
# ! [ -z ${VAR+_} ] returns true if VAR is declared at all
if ! [ -z "${_OLD_VIRTUAL_PATH+_}" ] ; then
PATH="$_OLD_VIRTUAL_PATH"
export PATH
unset _OLD_VIRTUAL_PATH
fi
if ! [ -z "${_OLD_VIRTUAL_PYTHONHOME+_}" ] ; then
PYTHONHOME="$_OLD_VIRTUAL_PYTHONHOME"
export PYTHONHOME
unset _OLD_VIRTUAL_PYTHONHOME
fi

# This should detect bash and zsh, which have a hash command that must
# be called to get it to forget past commands. Without forgetting
# past commands the $PATH changes we made may not be respected
if [ -n "${BASH-}" ] || [ -n "${ZSH_VERSION-}" ] ; then
hash -r 2>/dev/null
fi

if ! [ -z "${_OLD_VIRTUAL_PS1+_}" ] ; then
PS1="$_OLD_VIRTUAL_PS1"
export PS1
unset _OLD_VIRTUAL_PS1
fi

unset VIRTUAL_ENV
if [ ! "${1-}" = "nondestructive" ] ; then
# Self destruct!
unset -f deactivate
fi
}

# unset irrelevant variables
deactivate nondestructive

VIRTUAL_ENV="/home/eshaan/Desktop/CTFs/Abs0lut3Pwn4g3_CTF/encrypt-ctf-2019/web/100_Slash_Slash/handout/env"
export VIRTUAL_ENV

_OLD_VIRTUAL_PATH="$PATH"
PATH="$VIRTUAL_ENV/bin:$PATH"
export PATH

# unset PYTHONHOME if set
if ! [ -z "${PYTHONHOME+_}" ] ; then
_OLD_VIRTUAL_PYTHONHOME="$PYTHONHOME"
unset PYTHONHOME
fi

if [ -z "${VIRTUAL_ENV_DISABLE_PROMPT-}" ] ; then
_OLD_VIRTUAL_PS1="${PS1-}"
if [ "x" != x ] ; then
PS1="${PS1-}"
else
PS1="(`basename \"$VIRTUAL_ENV\"`) ${PS1-}"
fi
export PS1
fi

# Make sure to unalias pydoc if it's already there
alias pydoc 2>/dev/null >/dev/null && unalias pydoc || true

pydoc () {
python -m pydoc "$@"
}

# This should detect bash and zsh, which have a hash command that must
# be called to get it to forget past commands. Without forgetting
# past commands the $PATH changes we made may not be respected
if [ -n "${BASH-}" ] || [ -n "${ZSH_VERSION-}" ] ; then
hash -r 2>/dev/null
fi

# export $(echo RkxBRwo= | base64 -d)="ZW5jcnlwdENURntjb21tZW50c18mX2luZGVudGF0aW9uc19tYWtlc19qb2hubnlfYV9nb29kX3Byb2dyYW1tZXJ9Cg=="
```

`# export $(echo RkxBRwo= | base64 -d)="ZW5jcnlwdENURntjb21tZW50c18mX2luZGVudGF0aW9uc19tYWtlc19qb2hubnlfYV9nb29kX3Byb2dyYW1tZXJ9Cg=="`

`ZW5jcnlwdENURntjb21tZW50c18mX2luZGVudGF0aW9uc19tYWtlc19qb2hubnlfYV9nb29kX3Byb2dyYW1tZXJ9Cg==`

↓ decode by base64

`encryptCTF{comments_&_indentations_makes_johnny_a_good_programmer}`

---

## ★★important★★
They guess that they miss the combination of **ENV** and **shash shash** titles and problems...

**shash shash** → **/●●●/●●●**→**/whatsthetime/123** can be easily imagined!!