What is being tackled here is the amplification factor https://github.com/Phenomite/AMP-Research/tree/master/Port%2027015%20(%2B%20more%20ports)%20-%20SRCDS%20(Arma3%2C%20Gmod%2C%20CSGO%2C%20etc)
that means an attacker with a 100mbps connection at hand that allows spoofing could use srcds servers to achieve a 500mbps reflected attack towards a target big packets means the same attacker with a 100mbps connection would end up being able to only attack the target with potentially even less mbps then what he already had access to On Wed, 18 Nov 2020 at 04:23, David Parker <dpar...@utica.edu> wrote: > Moving the server side of the query handling to the GMS would solve all of > the issues for GSPs and others hosting the games. That makes perfect sense > to me. > > However, regarding the increased packet size (option #1), I'm a little > confused. If the idea here is that the servers expect really big packets > and reject anything too small, couldn't the asshats who launch these > attacks just update their existing code to pad the requests with zeros, and > we're back to the same problem? There's probably a piece to this that I'm > missing, and I apologize for my ignorance. > > Thanks! > Dave > > On Tue, Nov 17, 2020 at 4:53 PM Fletcher Dunn - fletcherd at > valvesoftware.com (via csgo_servers list) < > csgo_servers@list.valvesoftware.com> wrote: > >> >It depends now on what you're doing with SDR ;-). >> >> Yes, there are mechanisms to measure the latency to servers in known data >> centers, as well as to arbitrary hosts on the Internet using SDR P2P >> functionality. I was referring to the ordinary servers. >> >> -----Original Message----- >> From: Kyle Sanderson <kyle.l...@gmail.com> >> Sent: Tuesday, November 17, 2020 1:15 PM >> To: Fletcher Dunn <fletch...@valvesoftware.com> >> Cc: csgo_servers@list.valvesoftware.com >> Subject: Re: [Csgo_servers] RFC: Changes to the A2S_INFO protocol >> >> > I think some ping will always be necessary to measure the latency and >> > confirm UDP connectivity >> >> It depends now on what you're doing with SDR ;-). >> >> If you're planning on opening this up for optimized PoPs you already have >> the latency from the client, and the latency from the PoP to the server so >> you can return the sum there. One of the no-steam guys did this in like >> 2003 with his browser but he didn't control the PoPs. The latency was still >> off because he did addition of the requesting client >> + his master latency to the server then divided by two - with SDR you >> control the network (and the paths). >> >> > that the server is running >> >> Tweaking steamclient to be more happy with sharing alive updates (30s >> heartbeats) with the GMS would probably do the trick for stale >> information. It's not like it needs to be super up to date (although it >> could impact the "wait for a server slot" feature). >> >> Just a thought, anyway. >> >> Kyle. >> >> On Tue, Nov 17, 2020 at 12:23 PM Fletcher Dunn < >> fletch...@valvesoftware.com> wrote: >> > >> > The GMS does indeed have all of this information. >> > >> > Let me investigate moving more data to be in the GMS reply, instead of >> being returned in A2S_INFO. >> > >> > I think some ping will always be necessary to measure the latency and >> confirm UDP connectivity and that the server is running. But there are >> probably some simple changes that can be made to reduce the size of these >> replies significantly and move them to the GMS. >> > >> > -----Original Message----- >> > From: Kyle Sanderson <kyle.l...@gmail.com> >> > Sent: Tuesday, November 17, 2020 11:38 AM >> > To: csgo_servers@list.valvesoftware.com >> > Cc: Fletcher Dunn <fletch...@valvesoftware.com> >> > Subject: Re: [Csgo_servers] RFC: Changes to the A2S_INFO protocol >> > >> > > However, I am currently working on integrating SDR functionality >> > > with the server browser, and so while I am touching this code, it >> seemed like the right time to address this longstanding issue. >> > >> > Ahha! If we're already in there making other changes - I'd like to >> propose something else then. >> > >> > 1. Lets promote the GMS (if this still exists) to have all server >> information (players, rules, etc). >> > 2. Have steamclient default to leaving old queries enabled, but the >> games themselves with a convar to disable old queries by default. >> > 3. This way technically the client doesn't have to ping the server (I >> mean - it should still A2A_PING at some point), and tiny GSPs won't have to >> deal with conntrack as much. >> > >> > I think this is what was done with the old master > GMS flip(?) - same >> idea here. There can be a huge win because the GMS can immediately return >> all these results to the client (or pages - whatever), without destroying >> the conntrack table on bad home appliances. Simple stream, challenge, >> response with the full rendered list. "Steam Desktop Client" can still do >> the full query in the favourites list, but do a GMS query first for results >> and if it's missing try hitting it directly. >> > >> > WDYT? >> > >> > Kyle. >> > >> > On Tue, Nov 17, 2020 at 10:00 AM Fletcher Dunn - fletcherd at >> valvesoftware.com (via csgo_servers list) < >> csgo_servers@list.valvesoftware.com> wrote: >> > > >> > > John! Good to hear from all old folks from years ago! >> > > >> > > >> > > >> > > TL/DR: New proposal: the server requires all 3 connectionless packets >> from clients to be at least 1200 bytes. >> > > >> > > >> > > >> > > I’ve gotten similar feedback from a few people now. The only reason >> to consider allowing a smaller packet with a challenge is to give the >> client a way to reduce the bandwidth sent when pinging a ton of servers. >> But doing this would impair the ability to filter out these packets further >> out, and it is also more complicated to implement. (I wasn’t planning on >> changing the server browser in steamclient.dll to do it, I was just going >> to do the simple thing of padding the packet.) Given that it is 2020 The >> Year of Our Lord Gaben, probably the extra bandwidth needed to ping a bunch >> of servers is just not significant. >> > > >> > > >> > > >> > > Regarding 1200: although this technically maybe not OK according to >> RFCs from the mid 90’s, being larger than the absurdly small minimum IPv4 >> MTU, I believe it is OK in practice in 2020 TYOOLG, especially since the >> minimum MTU for IPv6 is 1280. In the SDR protocol used by CSGO and Dota, >> clients always initiate their communication with a 1200 byte packet, and >> that has not caused any problems. >> > > >> > > >> > > >> > > To Kyle Sanderson’s point: I realize that this is not the most >> pressing issue facing the Internet today. However, I am currently working >> on integrating SDR functionality with the server browser, and so while I am >> touching this code, it seemed like the right time to address this >> longstanding issue. However, Valve is very sensitive to breaking old >> games. It’s my understanding that this plan allows old games to continue >> to operate, even if the code cannot be updated. If I’m mistaken, let me >> know. >> > > >> > > >> > > >> > > From: John <lists.va...@nuclearfallout.net> >> > > Sent: Tuesday, November 17, 2020 9:38 AM >> > > To: csgo_servers@list.valvesoftware.com >> > > Cc: Fletcher Dunn <fletch...@valvesoftware.com> >> > > Subject: Re: [Csgo_servers] RFC: Changes to the A2S_INFO protocol >> > > >> > > >> > > >> > > Fletcher, >> > > >> > > This sounds like a reasonable idea. >> > > >> > > Of the two, requiring a large request (#1) might be best. Both #1 and >> #2 help with reflection attacks, but #1 also helps to mitigate directly >> spoofed query attacks on game servers. There is less overhead involved on >> the server side with rejecting an improperly sized packet than in >> generating a randomized challenge response and having to locally store that >> state; and, should the spoofer generate properly-sized packets, they would >> be limited to a lower overall packet rate (which also drastically reduces >> overhead on the server side). Further, an external firewall could easily >> drop improperly-formatted packets based on size, cutting out many attacks. >> > > >> > > (By the same token, connection and all other unsolicited packets >> > > should probably also be required to be large.) >> > > >> > > The only real downside would be that tools would need to be updated. >> I don't see a blocker there. >> > > >> > > The specific size of the packets isn't too important as long as it >> beats lowest-common-denominator MTUs. 800-1200 should be fine. >> > > >> > > One other consideration here is whether this can be coupled with >> changes designed to mitigate the negatives of proxied responses (some hosts >> have taken to advertising their prefixes from multiple PoPs and proxying >> query responses in order to fake lower latencies, which degrades the player >> experience). I can't immediately think of a good mechanism for that in the >> query protocol itself; the primary way to deal with it would seem to be at >> the global level, by penalizing servers whose latencies are measured to be >> low from multiple locations in an impossible way. >> > > >> > > -John >> > > >> > > On 11/16/2020 5:21 PM, Fletcher Dunn - fletcherd at valvesoftware.com >> (via csgo_servers list) wrote: >> > > >> > > Hello! >> > > >> > > >> > > >> > > Over the next couple of months we will be releasing some changes to >> how servers and clients using steamclent.so/dll handle the venerable >> Source engine A2S_INFO message used by the server browser. This includes >> the Steam client server browser, all Source engine games, and all Steam >> games using the ISteamMatchmaking API. The purpose of these changes is a >> long overdue fix for a reflection attack vulnerability. >> > > >> > > >> > > >> > > This email is to let you know what those plans are and to solicit >> your feedback. Fixing the vulnerability requires changing the protocol and >> will necessarily break existing third party utilities that speak the >> protocol. >> > > >> > > >> > > >> > > Currently, the A2S_INFO packet looks like this: >> > > >> > > 4 bytes: 0xFFFFFFFF >> > > >> > > 1 byte: 0x54 (A2S_INFO packet type identifier) >> > > >> > > 20 bytes: "Source Engine Query\0" >> > > >> > > >> > > >> > > The proposal is for clients to modify the A2S_INFO packet they send >> in one of two ways: >> > > >> > > >> > > >> > > Option 1: Pad the message with zeros, so that the request is larger >> than the reply. The passes size is TBD, but it will probably be at least >> 800 bytes, and perhaps as high as 1200. Feedback is requested concerning >> this size. >> > > >> > > >> > > >> > > Option 2: Append a 4-byte anti-spoofing challenge obtained using the >> existing A2S_PLAYER or A2S_RULES messages. >> > > >> > > >> > > >> > > Note that both options produce a packet that is acceptable to the >> current code in steamclient.so/dll. However, any custom handlers might >> have stricter behavior, and will need to be updated to be aware than >> “extra” data might appear after the end of the magic string in packets from >> legitimate clients. >> > > >> > > >> > > >> > > Once all clients are using one of these two options, a server wishing >> to avoid being vulnerable to reflection attacks could drop any A2S_INFO >> packets below a minimum size without a challenge. >> > > >> > > >> > > >> > > The changes would be deployed as follows: >> > > >> > > >> > > >> > > 1. First, we will release a new Steam client that sends >> A2S_INFO messages padding to a minimum size. (Option #1 above.) Since it >> takes time for Steam client updates to roll out to all Steam users, and for >> third parties to change their code to make queries in the new format, we >> will not change the server to require the new format by default. However, >> the server code will be updated to look for an environment variable that >> can be used to opt into the new, stricter behavior. This is so that third >> parties can test their clients to make sure they are compliant with the new >> server code. >> > > >> > > 2. As more clients upgrade to the new code and third party >> tools are updated to send queries in the new format, server operators may >> elect to opt into the new behavior at their discretion using the >> environment variable. >> > > >> > > 3. After some time has passed (and we have posted several >> warnings on this mailing list), we will ship a new steamclient.so/.dll >> that has the strict behavior enabled by default. A different environment >> variable can be used to use the older, more permissive behaviour. >> > > >> > > >> > > >> > > If you have any concerns or feedback about this change, please reply >> to this steam post: >> > > >> > > https://steamcommunity.com/discussions/forum/14/2989789048633291344/ >> > > >> > > >> > > >> > > After feedback has been collected and details finalized, I’ll post >> again with more technical details about the changes that are going to be >> made. >> > > >> > > _______________________________________________ >> > > To unsubscribe, edit your list preferences, or view the list >> > > archives, please visit: >> > > https://list.valvesoftware.com/ >> > > >> > > >> > > >> > > _______________________________________________ >> > > To unsubscribe, edit your list preferences, or view the list >> > > archives, please visit: >> > > https://list.valvesoftware.com/ >> > >> >> _______________________________________________ >> To unsubscribe, edit your list preferences, or view the list archives, >> please visit: >> https://list.valvesoftware.com/ > > > > -- > Dave Parker '11 > Database & Systems Administrator > Utica College > Integrated Information Technology Services > (315) 792-3229 > Registered Linux User #408177 > > _______________________________________________ > To unsubscribe, edit your list preferences, or view the list archives, > please visit: > https://list.valvesoftware.com/ > _______________________________________________ To unsubscribe, edit your list preferences, or view the list archives, please visit: https://list.valvesoftware.com/
