Re: [quicwg/base-drafts] Increase resilience to spoofed Version Negotiation packets (#524)

[janaiyengar <[e-mail]>]

janaiyengar commented on this pull request.



> -uses on every packet it sends.  Packets MUST continue to use long headers and
-MUST include the new negotiated protocol version.
+A client MUST discard a Version Negotiation packet that does not contain Packet
+Number and Version fields that match those fields in a packet that the client
+previously sent.  This doesn't guarantee that the Version Negotiation packet is
+genuine, but it reduces the chances that the packet is spoofed.
+
+A client that receives a valid Version Negotiation packet selects an acceptable
+protocol version from those listed by the server.  The client then reattempts to
+create a connection using that version.  Though the contents of a packet might
+not change in response to version negotiation, a client MUST choose a new packet
+number it uses on every packet it sends.
+
+If the server does not list an acceptable version, the client MAY ignore the
+Version Negotiation packet.  This might reduce the likelihood that a spoofed
+Version Negotiation packet can be used to disrupt connection establishment.

+1. I would expect the common case to be mismatch, since an attacker can easily generate a VN packet that supports a large number of known versions (minus the client's chosen).

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