题目链接

查看源码

发现 <!-- /source -->

访问下载得到python源代码

代码审计

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
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
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)

代码逻辑:

  1. 上传的文件名如果包含 “.”,则报错
  2. 上传成功的文件会存入uploads 文件夹中并生成一个uuid在file路径下
  3. 访问file/<id> 时找到对应文件名,然后拼接成 uploads/filename ,读取文件内容

分析

os.path.join() 函数存在绝对路径拼接漏洞

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

exp

上传任意文件 然后抓包将文件名改为 “/flag”,进行路径拼接时uploads/被删去,只剩下”/flag”;跳转到 "/file/<uuid>" 即可查看flag

⬆︎TOP