Django Documentation
csrf保护基于以下:
1, 一个CSRF cookie基于一个随机生成的值,其他网站无法得到,次cookie有CsrfViewMiddleware产生.它与每个调用django.middleware.csrf.get_token()(这是一个用于取回CSRF token的方法)的响应一起发送,如果它尚未在请求上设置的话.
为了放置BREACH攻击,token不仅仅是比吗,随机的salt被置于secret之前并用来加密它,出于安全原因,每次用户登陆都会更改密钥的值.
CsrfViewMiddleware.process_request
class CsrfViewMiddleware(MiddlewareMixin):
def process_request(self, request):
csrf_token = self._get_token(request)
# 第一次访问, csrf_token返回None,
if csrf_token is not None:
request.META["CSRF_COOKIE"] = csrf_token
# request.META是一个python字典,包含了所有本次Http请求的Header信息,比如用户IP地址和用户Agent(通常是浏览器的名称版本号).
settings = Lazysettins()
这是一个懒加载
方法_get_token,从名字上看就是获取token, _get_token在后面多处地方用到
def _get_token(self, request):
# CSRF_USE_SESSIONS在django/conf/global_settings.py，默认为False,执行else
if settings.CSRF_USE_SESSIONS:
try:
return request.session.get(CSRF_SESSION_KEY)
except AttributeError:
raise ImproperlyConfigured(
‘CSRF_USE_SESSIONS is enabled, but request.session is not ‘
‘set. SessionMiddleware must appear before CsrfViewMiddleware ‘
‘in MIDDLEWARE%s.‘ % (‘_CLASSES‘ if settings.MIDDLEWARE is None else ‘‘)
)
else:
try:
cookie_token = request.COOKIES[settings.CSRF_COOKIE_NAME]
# CSRF_SESSION_KEY= "csrftoken"
except KeyError:
# 第一次访问的时候 request.COOKIES = {},所以直接返回
return None
csrf_token = _sanitize_token(cookie_token)
# csrf 对不上 cookie里 的 token，标记csrf_cookie_needs_reset=True，
# 在process_response的方法中判定
if csrf_token != cookie_token:
# Cookie token needed to be replaced;
# the cookie needs to be reset.
request.csrf_cookie_needs_reset = True
return csrf_token
CSRF_SECRET_LENGTH = 32
CSRF_TOKEN_LENGTH = 2 * CSRF_SECRET_LENGTH
def _sanitize_token(token):
# Allow only ASCII alphanumerics
if re.search(‘[^a-zA-Z0-9]‘, force_text(token)):
return _get_new_csrf_token()
先跳转到_get_new_csrf_token(),看他的生成方法
def _get_new_csrf_token():
return _salt_cipher_secret(_get_new_csrf_string())
CSRF_SECRET_LENGTH = 32
CSRF_TOKEN_LENGTH = 2 * CSRF_SECRET_LENGTH
def _get_new_csrf_string():
return get_random_string(CSRF_SECRET_LENGTH, allowed_chars=CSRF_ALLOWED_CHARS)
def _salt_cipher_secret(secret):
"""
Given a secret (assumed to be a string of CSRF_ALLOWED_CHARS), generate a
token by adding a salt and using it to encrypt the secret.
给定一个secret(假设是一串 CSRF_ALLOWED_CHARS), 通过添加一个随机生成值并使用它来加密secret生成一个token
"""
salt = _get_new_csrf_string()
chars = CSRF_ALLOWED_CHARS
pairs = zip((chars.index(x) for x in secret), (chars.index(x) for x in salt))
cipher = ‘‘.join(chars[(x + y) % len(chars)] for x, y in pairs)
return salt + cipher
文件位置:django/utils/crypto.py
def get_random_string(length=12,
allowed_chars=‘abcdefghijklmnopqrstuvwxyz‘
‘ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789‘):
"""
Returns a securely generated random string. 返回安全生成的随机字符串
The default length of 12 with the a-z, A-Z, 0-9 character set returns
a 71-bit value. log_2((26+26+10)^12) =~ 71 bits
"""
if not using_sysrandom:
# This is ugly, and a hack, but it makes things better than
# the alternative of predictability. This re-seeds the PRNG
# using a value that is hard for an attacker to predict, every
# time a random string is required. This may change the
# properties of the chosen random sequence slightly, but this
# is better than absolute predictability.
random.seed(
hashlib.sha256(
("%s%s%s" % (
random.getstate(),
time.time(),
settings.SECRET_KEY)).encode(‘utf-8‘)
).digest())
return ‘‘.join(random.choice(allowed_chars) for i in range(length))
返回的是一个随机的字符串
# 接上面的def _sanitize_token
elif len(token) == CSRF_TOKEN_LENGTH:
return token
elif len(token) == CSRF_SECRET_LENGTH:
# Older Django versions set cookies to values of CSRF_SECRET_LENGTH
# alphanumeric characters. For backwards compatibility, accept
# such values as unsalted secrets.
# It‘s easier to salt here and be consistent later, rather than add
# different code paths in the checks, although that might be a tad more
# efficient.
# 较旧的Django版本将cookie设置为CSRF_SECRET_LENGTH字母数字字符的值.为了向后
# 兼容,接受诸如无保密秘密之类的值.这里更容易加盐并在以后保持一致,而不是在检查中
# 添加不同的代码路径, 尽管这可能会更有效
return _salt_cipher_secret(token)
return _get_new_csrf_token()
def process_view(self, request, callback, callback_args, callback_kwargs):
if getattr(request, ‘csrf_processing_done‘, False):
return None
# Wait until request.META["CSRF_COOKIE"] has been manipulated before
# bailing out, so that get_token still works
# 如果装饰器@csrf_exempt生效,则不处理
if getattr(callback, ‘csrf_exempt‘, False):
return None
# Assume that anything not defined as ‘safe‘ by RFC7231 needs protection
if request.method not in (‘GET‘, ‘HEAD‘, ‘OPTIONS‘, ‘TRACE‘):
if getattr(request, ‘_dont_enforce_csrf_checks‘, False):
# Mechanism to turn off CSRF checks for test suite.
# It comes after the creation of CSRF cookies, so that
# everything else continues to work exactly the same
# (e.g. cookies are sent, etc.), but before any
# branches that call reject().
# 关闭CSRF检查测试套件的机制.在创建CSRF cookie之后,所以
# 其他所有内容继续完全相同(例如发送cookie等),但在调用
# reject()的任何分支之前
return self._accept(request)
def _accept(self, request):
# Avoid checking the request twice by adding a custom attribute to
# request. This will be relevant when both decorator and middleware
# are used.
request.csrf_processing_done = True
return None
接上面的CsrfViewMiddleware.process_view的代码
# is_secure 如果请求是安全的，返回True，意味着发出的是HTTPS请求。
if request.is_secure():
referer = request.META.get(‘HTTP_REFERER‘)
if referer is None:
return self._reject(request, REASON_NO_REFERER)
# _reject就是csrf验证不通过，因为reffer为空
返回一个Forbidden的代码
def _reject(self, request, reason):
logger.warning(
‘Forbidden (%s): %s‘, reason, request.path,
extra={
‘status_code‘: 403,
‘request‘: request,
}
)
return _get_failure_view()(request, reason=reason)
referer = urlparse(referer)
# referer.scheme: 请求的协议,一般为http或者https
# referer.netloc: host域名
# Make sure we have a valid URL for Referer.
# 确保我们在referer中有一个有效的URL
if ‘‘ in (referer.scheme, referer.netloc):
return self._reject(request, REASON_MALFORMED_REFERER)
# Ensure that our Referer is also secure.
if referer.scheme != ‘https‘:
return self._reject(request, REASON_INSECURE_REFERER)
# If there isn‘t a CSRF_COOKIE_DOMAIN, require an exact match
# match on host:port. If not, obey the cookie rules (or those
# for the session cookie, if CSRF_USE_SESSIONS).
good_referer = (
settings.SESSION_COOKIE_DOMAIN
if settings.CSRF_USE_SESSIONS
else settings.CSRF_COOKIE_DOMAIN
)
if good_referer is not None:
server_port = request.get_port()
if server_port not in (‘443‘, ‘80‘):
good_referer = ‘%s:%s‘ % (good_referer, server_port)
else:
# request.get_host() includes the port.
good_referer = request.get_host()
# Here we generate a list of all acceptable HTTP referers,
# including the current host since that has been validated
# upstream.
# 在这里,我们生成所有可能接受HTTP引用的列表,包括当前主机,因为
# 它已经在上游验证.
good_hosts = list(settings.CSRF_TRUSTED_ORIGINS)
good_hosts.append(good_referer)
# 禁止跨域
if not any(is_same_domain(referer.netloc, host) for host in good_hosts):
reason = REASON_BAD_REFERER % referer.geturl()
return self._reject(request, reason)
csrf_token = request.META.get(‘CSRF_COOKIE‘)
if csrf_token is None:
# No CSRF cookie. For POST requests, we insist on a CSRF cookie,
# and in this way we can avoid all CSRF attacks, including login
# CSRF.
return self._reject(request, REASON_NO_CSRF_COOKIE)
# Check non-cookie token for match.
request_csrf_token = ""
if request.method == "POST":
try:
# request.POST.get()相当于获取request.POST["csrfmiddlewaretoken"]
# 如果出错就返回‘‘, 这里的csrfmiddlewaretoken是提交的表单中的值,在模板
# 中用{% csrf_token %}生成
request_csrf_token = request.POST.get(‘csrfmiddlewaretoken‘, ‘‘)
except IOError:
# Handle a broken connection before we‘ve completed reading
# the POST data. process_view shouldn‘t raise any
# exceptions, so we‘ll ignore and serve the user a 403
# (assuming they‘re still listening, which they probably
# aren‘t because of the error).
# 在我们完成读取POST数据之前处理断开的连接.
# process_view不应该引发任何exception.一次我们将忽略并返回403
pass
if request_csrf_token == "":
# Fall back to X-CSRFToken, to make things easier for AJAX,
# and possible for PUT/DELETE.
# ajax中使用"X-CSRFToken"
# CERF_HEADER_NAME = "HTTP_X_CSRFTOKEN"
request_csrf_token = request.META.get(settings.CSRF_HEADER_NAME, ‘‘)
request_csrf_token = _sanitize_token(request_csrf_token)
# 对比两个csrf_token, 一个是表单里隐藏的csrfmiddlewaretoken
# 或者ajax的header: X_CSRFTOKEN, 另一个是自带的cookies里面的csrf_token
if not _compare_salted_tokens(request_csrf_token, csrf_token):
# 匹配不会就拒绝
return self._reject(request, REASON_BAD_TOKEN)
return self._accept(request)
def _compare_salted_tokens(request_csrf_token, csrf_token):
# Assume both arguments are sanitized -- that is, strings of
# length CSRF_TOKEN_LENGTH, all CSRF_ALLOWED_CHARS.
return constant_time_compare(
_unsalt_cipher_token(request_csrf_token),
_unsalt_cipher_token(csrf_token),
)
def _unsalt_cipher_token(token):
"""
Given a token (assumed to be a string of CSRF_ALLOWED_CHARS, of length
CSRF_TOKEN_LENGTH, and that its first half is a salt), use it to decrypt
the second half to produce the original secret.
"""
salt = token[:CSRF_SECRET_LENGTH]
token = token[CSRF_SECRET_LENGTH:]
chars = CSRF_ALLOWED_CHARS
pairs = zip((chars.index(x) for x in token), (chars.index(x) for x in salt))
secret = ‘‘.join(chars[x - y] for x, y in pairs) # Note negative values are ok
return secret
def _accept(self, request):
# Avoid checking the request twice by adding a custom attribute to
# request. This will be relevant when both decorator and middleware
# are used.
request.csrf_processing_done = True
return None
get_token(important)
get_token是在外部调用,由Template中的{% csrf_token %}触发,由request的cookie不同做出不同的反应.
def get_token(request):
"""
Returns the CSRF token required for a POST form. The token is an
alphanumeric value. A new token is created if one is not already set.
A side effect of calling this function is to make the csrf_protect
decorator and the CsrfViewMiddleware add a CSRF cookie and a ‘Vary: Cookie‘
header to the outgoing response. For this reason, you may need to use this
function lazily, as is done by the csrf context processor.
"""
if "CSRF_COOKIE" not in request.META:
# 如果request中不存在csrf, 先生成一个新的secret, 加密赋值到META["CSRF_COOKIE"]
# 后面用来放到set_cookie之中
csrf_secret = _get_new_csrf_string()
request.META["CSRF_COOKIE"] = _salt_cipher_secret(csrf_secret)
else:
csrf_secret = _unsalt_cipher_token(request.META["CSRF_COOKIE"])
request.META["CSRF_COOKIE_USED"] = True
return _salt_cipher_secret(csrf_secret)
上面返回的一个加密secret将会被填充进入<input type="hidden" name="csrfmiddlewaretoken" value="{}">, value里面,随着表单一起提交并和cookie之中的csrf_token比较
CsrfViewMiddleware.process_response
def process_response(self, request, response):
if not getattr(request, ‘csrf_cookie_needs_reset‘, False):
if getattr(response, ‘csrf_cookie_set‘, False):
return response
if not request.META.get("CSRF_COOKIE_USED", False):
return response
# Set the CSRF cookie even if it‘s already set, so we renew
# the expiry timer.
self._set_token(request, response)
response.csrf_cookie_set = True
return response
# 设置token
def _set_token(self, request, response):
if settings.CSRF_USE_SESSIONS:
request.session[CSRF_SESSION_KEY] = request.META[‘CSRF_COOKIE‘]
else:
response.set_cookie(
settings.CSRF_COOKIE_NAME,
# request.META[‘CSRF_COOKIE‘]就是在上面赋值的
request.META[‘CSRF_COOKIE‘],
max_age=settings.CSRF_COOKIE_AGE,
domain=settings.CSRF_COOKIE_DOMAIN,
path=settings.CSRF_COOKIE_PATH,
secure=settings.CSRF_COOKIE_SECURE,
httponly=settings.CSRF_COOKIE_HTTPONLY,
)
# Set the Vary header since content varies with the CSRF cookie.
patch_vary_headers(response, (‘Cookie‘,))
总结:
第一个访问页面
首先第一次访问页面,Template中的{% csrf_token %}会启动get_token(不是私有方法), 产生一个csrf_secret的值
这个值在_salt_cipher_secret中随机产生一个与csrf_secret长度相同的salt,利用salt加密csrf_secret, 两个字符串拼接形成csrf_token, request.META["CSRF_COOKIE"] = csrf_token并设置cookie里面
get_token返回的用随机生成的例外一个salt加密csrf_secret,同样拼接返回放入process_view进行解密,比对,如果解密出来的数值不同直接返回_reject()
- 所有传出POST表单中都有一个名为
csrfmiddlewaretoken的隐藏表单字段。此字段的值同样是秘密的值。salt添加到它并用于加扰它。每次调用get_token（）时都会重新生成salt，以便在每个此类响应中更改表单字段值。这部分由template的{% csrf_token %}完成。 - 对于未使用
HTTPGET，HEAD，OPTIONS或TRACE的所有传入请求，必须带有CSRF cookie，并且csrfmiddlewaretoken字段必须存在且正确。如果不是，用户将收到403错误。
验证csrfmiddlewaretoken字段值时，只将secret而不是整个token与cookie值中的secret进行比较。这允许使用不断变化的token。虽然每个请求都可以使用自己的token，但secret仍然是所有人共同的。
此检查由CsrfViewMiddleware完成。 - 此外，对于
HTTPS请求，严格的引用检查由CsrfViewMiddleware完成。这意味着即使子域可以在您的域上设置或修改cookie，它也不能强制用户发布到您的应用程序，因为该请求不会来自您自己的确切域。 这也解决了在使用会话独立秘密时在HTTPS下可能发生的中间人攻击，因为即使在HTTPS下与站点通信时，HTTP Set-Cookie标头（不幸）也被客户接受了。 。 （对HTTP请求不进行引用检查，因为在HTTP下，Referer头的存在不够可靠。） 如果设置了CSRF_COOKIE_DOMAIN设置，则会将引用者与其进行比较。此设置支持子域。例如，CSRF_COOKIE_DOMAIN =‘.example.com‘将允许来自www.example.com和api.example.com的POST请求。如果未设置该设置，则referer必须与HTTP Host标头匹配。 可以使用CSRF_TRUSTED_ORIGINS设置将已接受的引用扩展到当前主机或cookie域之外。
原文地址：https://www.cnblogs.com/chenrun/p/9676010.html
时间： 2024-10-19 20:02:24