I have reviewed this document as part of the security directorate's 
ongoing effort to review all IETF documents being processed by the 
IESG.  These comments were written primarily for the benefit of the 
security area directors.  Document editors and WG chairs should treat 
these comments just like any other last call comments.

Document: draft-ietf-quic-version-negotiation-10
Reviewer: Joey Salazar
The summary of the review is: Ready with nits

Major Concerns: None

Minor Concerns: None

Nits:

Section 2.1: "it SHALL select a mutually supported version and sends[…]"
s/sends/send/
		
Section 2.4: This section states "the connection attempt prior to receiving the Version Negotiation packet is distinct from the connection with the incompatible version that follows". According to text in Section 2.1 "it SHALL select a mutually supported version and sends a new first flight with that version - this version is now the negotiated version", Section 2.4 could say "from the connection with the negotiated version that follows" instead.
	
Section 7: s/Since at the time of writing QUIC version 1/Since, at the time of writing, QUIC version 1/

Section 8: For clarity of reading, this section could be placed after Section 4. Version Downgrade Prevention

Section 9: The security of the mechanism relying on the security of the weakest common version seems clear, yet a bit more description on "but more analysis is still needed here" would be good, perhaps pointing to what other vulnerabilities could be expected/analyzed, or whether cross-protocol attacks could still take place.