Server Hide Reference $Id: serverhide.txt,v 1.2 2004/02/02 23:42:56 ircd Exp $ Copyright (c) 2001 by ircd-hybrid team ---------------------------------------------------------------------- Due to pressures from abusers, the Hybrid developers have created a set of options to limit what users can and cannot do on the server. Each option can be enabled or disabled at runtime. This document describes the Hybrid 7 implementation of the server hiding ideas originated by (and credited to) numerous people. * LINKS as a file: This option is always enabled. It will generate a file at a certain interval, defined by the links_delay in ircd.conf, that contains the current LINKS data. This data is sent to users whenever a LINKS is requested. Opers will always see the current server structure. The file that the LINKS data is stored in is by default etc/links.txt. The benefits of this are that transient splits will not be seen by users issuing LINKS commands, and if a server is split, users can still see what other servers are normally available. * Flattened LINKS: This option forces every server to look as if it is connected to the local server. Users will see a flat LINKS tree. The benefit to using LINKS flattening is that users cannot get information on how servers are routed. The flatten_links in the serverhide {} block in the ircd.conf controls this feature. As a side effect, all netsplit quit messages will appear to originate from the local server. +--------------------------------------------------------------------+ | Flattened LINKS is needed for any network that uses the hidden hub | | option. See below for more details. | +--------------------------------------------------------------------+ * Hidden server option: This option will hide the server from a flattened LINKS list on other servers. Opers will of course see the true routing of the network. This is controlled by the hidden option in ircd.conf. +--------------------------------------------------------------------+ | Technically, this code is a hack. With this option enabled, the | | server will prepend '(H) ' to the server info field when | | connecting to other servers. Other servers must understand that | | the (H) means hidden. | +--------------------------------------------------------------------+ * The allow_hidden option is needed to allow servers to use the hidden server option described above. * The hide_servers option forces the server to not be shown when a user issues WHOIS and other commands which may show what server a user is on. Local user counts, as normally displayed in LUSERS, USERS, and the 255 numeric, will be shown with the same values as the global counts. Displaying it this way will help protect servers and avoid breaking scripts that depend on the 265 and 266 numerics on connect. To be effective, this option must be used network wide. * The disable_remote_commands option takes care of most of the remaining issues. These include, for example, ADMIN some.hub.server, VERSION someuser, and similar commands. A server with this option enabled will only prevent local users from issuing remote commands. Remote users will not be affected. Remote WHOIS is not blocked. It is, however, restricted to only querying WHOIS nick nick. The ircd will disregard the server parameter and always use queried nick. * The disable_local_channels option will not allow users to join local &channels. This option is a little extreme, taking away a lot of user privilege. It was created to handle the possible hole in server hide shown below. * All server modes appear to originate from the server you are using. This feature is not tunable; and opers also do not see the real server setting the mode. Each item is briefly described in the serverhide {} block in ircd.conf. ---------------------------------------------------------------------- Questions and Answers &channels and remote WHOIS I brought this up a short while ago; and there are some holes in server hide at the present time with local channels. The issue I raised, if a user is known to be in a local channel, issuing WHOIS servera nick, WHOIS serverb nick, etc. until the local channel is seen in the WHOIS data does not exist. With disable_remote_commands enabled, the WHOIS is still sent (in order to see idle time and the away message) but the server queried will always be the server the user is on. The user can never use remote WHOIS to determine the server a user is on. If an abuser knows that a user is on a specific &channel, they could still connect to each server until they find the server showing the user in the local channel in a local WHOIS. The disable_local_channels option has been created to handle this risk. ---------------------------------------------------------------------- Using Non-QS Compliant Hubs The flattened LINKS option will, as a side effect, display all user QUIT's due to network splits in the following format: :user QUIT :your.server.name *.split This works extremely well as long as all servers on your network are compliant with the QS capability, which sends a single SQUIT to the network when a server (or tree of servers) splits. All quit messages are generated on the local server. Certain older servers do not have this ability, and as such will generate their own quit messages for users who left because of the split. This can cause leaks in the hub server names and the structure of the network. A quick example is the following network structure: servA(Hyb7) --- hubA(nonQS) --- servB(not-important) When servB splits from hubA, hubA will generate a QUIT command for every user on servB (and anything behind servB). Since the QUIT message was not created on your server, with server hiding enabled, the QUIT message will contain the real server names. The only way to prevent this leak on a network is to only use hubs supporting the QS capability. Hybrid 6, Hybrid 7, and csircd all are currently running daemons that support QS. Hybrid 5 and 2.8.21+CSr servers do not support QS, and will leak server names (and therefore routing information) on splits. ---------------------------------------------------------------------- Index XXX - Fill me in with other questions and possible issues