security - 为什么 WebSockets 被屏蔽了？

Question

我按照 MDN 在 Writing a WebSocket server 上提供的指南进行操作。 , 该指南非常简单易懂...

但是，在遵循本教程后，我遇到了发送来自客户端的 WebSocket 消息的框架:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-------+-+-------------+-------------------------------+
|F|R|R|R| opcode|M| Payload len | Extended payload length |
|I|S|S|S| (4) |A| (7) | (16/64) |
|N|V|V|V| |S| | (if payload len==126/127) |
| |1|2|3| |K| | |
+-+-+-+-+-------+-+-------------+ - - - - - - - - - - - - - - - +
| Extended payload length continued, if payload len == 127 |
+ - - - - - - - - - - - - - - - +-------------------------------+
| |Masking-key, if MASK set to 1 |
+-------------------------------+-------------------------------+
| Masking-key (continued) | Payload Data |
+-------------------------------- - - - - - - - - - - - - - - - +
: Payload Data continued ... :
+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +
| Payload Data continued ... |
+---------------------------------------------------------------+

在制作了一些函数来正确地取消屏蔽客户端发送的数据和帧之后，这让我想知道为什么数据甚至一开始就被屏蔽了。我的意思是，您不必屏蔽从服务器发送的数据...

如果有人出于不良原因获取数据，则取消屏蔽可能相对容易，因为屏蔽 key 包含在整个消息中。或者即使他们没有 key ，帧中的掩码 key 也只有 2 个字节长。由于 key 非常非常小，因此有人可以轻松地揭开数据的面纱。

我想知道为什么要屏蔽数据的另一个原因是，您可以通过在 TLS/SSL 和 HTTPS 上使用 WSS(WebSockets Secure)来更好地保护您的 WebSocket 数据。

我是否错过了为什么 WebSocket 被屏蔽的重点？似乎它只是增加了毫无意义的努力来揭露客户端发送的数据，而它并没有增加任何安全性。

Answer 1

实际上是权威的 RFC，RFC 6455 The WebSocket Protocol ，有解释。我在这里引用它:

 10.3.  Attacks On Infrastructure (Masking)

   In addition to endpoints being the target of attacks via WebSockets,
   other parts of web infrastructure, such as proxies, may be the
   subject of an attack.

   As this protocol was being developed, an experiment was conducted to
   demonstrate a class of attacks on proxies that led to the poisoning
   of caching proxies deployed in the wild [TALKING].  The general form
   of the attack was to establish a connection to a server under the
   "attacker's" control, perform an UPGRADE on the HTTP connection
   similar to what the WebSocket Protocol does to establish a
   connection, and subsequently send data over that UPGRADEd connection
   that looked like a GET request for a specific known resource (which
   in an attack would likely be something like a widely deployed script
   for tracking hits or a resource on an ad-serving network).  The
   remote server would respond with something that looked like a
   response to the fake GET request, and this response would be cached
   by a nonzero percentage of deployed intermediaries, thus poisoning
   the cache.  The net effect of this attack would be that if a user
   could be convinced to visit a website the attacker controlled, the
   attacker could potentially poison the cache for that user and other
   users behind the same cache and run malicious script on other
   origins, compromising the web security model.

   To avoid such attacks on deployed intermediaries, it is not
   sufficient to prefix application-supplied data with framing that is
   not compliant with HTTP, as it is not possible to exhaustively
   discover and test that each nonconformant intermediary does not skip
   such non-HTTP framing and act incorrectly on the frame payload.
   Thus, the defense adopted is to mask all data from the client to the
   server, so that the remote script (attacker) does not have control
   over how the data being sent appears on the wire and thus cannot
   construct a message that could be misinterpreted by an intermediary
   as an HTTP request.

   Clients MUST choose a new masking key for each frame, using an
   algorithm that cannot be predicted by end applications that provide
   data.  For example, each masking could be drawn from a
   cryptographically strong random number generator.  If the same key is
   used or a decipherable pattern exists for how the next key is chosen,
   the attacker can send a message that, when masked, could appear to be
   an HTTP request (by taking the message the attacker wishes to see on
   the wire and masking it with the next masking key to be used, the
   masking key will effectively unmask the data when the client applies
   it).

   It is also necessary that once the transmission of a frame from a
   client has begun, the payload (application-supplied data) of that
   frame must not be capable of being modified by the application.
   Otherwise, an attacker could send a long frame where the initial data
   was a known value (such as all zeros), compute the masking key being
   used upon receipt of the first part of the data, and then modify the
   data that is yet to be sent in the frame to appear as an HTTP request
   when masked.  (This is essentially the same problem described in the
   previous paragraph with using a known or predictable masking key.)
   If additional data is to be sent or data to be sent is somehow
   changed, that new or changed data must be sent in a new frame and
   thus with a new masking key.  In short, once transmission of a frame
   begins, the contents must not be modifiable by the remote script
   (application).

   The threat model being protected against is one in which the client
   sends data that appears to be an HTTP request.  As such, the channel
   that needs to be masked is the data from the client to the server.
   The data from the server to the client can be made to look like a
   response, but to accomplish this request, the client must also be
   able to forge a request.  As such, it was not deemed necessary to
   mask data in both directions (the data from the server to the client
   is not masked).

   Despite the protection provided by masking, non-compliant HTTP
   proxies will still be vulnerable to poisoning attacks of this type by
   clients and servers that do not apply masking.