from flask import Flask, request, redirect, g, send_from_directory
import sqlite3
import os
import uuid
app = Flask(__name__)
SCHEMA = """CREATE TABLE files (
id text primary key,
path text
);
"""
def db():
g_db = getattr(g, '_database', None)
if g_db is None:
g_db = g._database = sqlite3.connect("database.db")
return g_db
@app.before_first_request
def setup():
os.remove("database.db")
cur = db().cursor()
cur.executescript(SCHEMA)
@app.route('/')
def hello_world():
return """<!DOCTYPE html>
<html>
<body>
<form action="/upload" method="post" enctype="multipart/form-data">
Select image to upload:
<input type="file" name="file">
<input type="submit" value="Upload File" name="submit">
</form>
<!-- /source -->
</body>
</html>"""
@app.route('/source')
def source():
return send_from_directory(directory="/var/www/html/", path="www.zip", as_attachment=True)
@app.route('/upload', methods=['POST'])
def upload():
if 'file' not in request.files:
return redirect('/')
file = request.files['file']
if "." in file.filename:
return "Bad filename!", 403
conn = db()
cur = conn.cursor()
uid = uuid.uuid4().hex #生成uid
try:
cur.execute("insert into files (id, path) values (?, ?)", (uid, file.filename,))
except sqlite3.IntegrityError:
return "Duplicate file"
conn.commit()
file.save('uploads/' + file.filename)
return redirect('/file/' + uid)
@app.route('/file/<id>')
def file(id):
conn = db()
cur = conn.cursor()
cur.execute("select path from files where id=?", (id,))
res = cur.fetchone()
if res is None:
return "File not found", 404
# print(res[0])
with open(os.path.join("uploads/", res[0]), "r") as f:
return f.read()
if __name__ == '__main__':
app.run(host='0.0.0.0', port=80)
def upload() 要求上传的文件不能有后缀，且文件名前会拼接一个前缀upload/，使得输出的文件只能是在目录upload/下的，这里就涉及到os.path.join()的绝对路径拼接漏洞：
绝对路径拼接漏洞
os.path.join(path,*paths)函数用于将多个文件路径连接成一个组合的路径。第一个函数通常包含了基础路径，而之后的每个参数被当作组件拼接到基础路径之后。
然而，这个函数有一个少有人知的特性，如果拼接的某个路径以 / 开头，那么包括基础路径在内的所有前缀路径都将被删除，该路径将视为绝对路径。
with open(os.path.join("uploads/", res[0]), "r") as f: return f.read()
就是说传/flag，那么之前的upload/就会删除，就直接读取了根目录下的flag文件。抓包将文件名改为/flag。
直接访问得到的路径，获得flag：
