NAME user-rawip-attack AUTHOR Marc SCHAEFER <schaeferat_private> with the help of Alan COX (for the fix) and of Andreas Trottmann <andreas.trottmannat_private> for the work-around idea. VERSION $Id: user-raw-IP,v 1.3 1999/10/22 08:33:10 schaefer Exp $ ABSTRACT Forged packets can be send out from a Linux system, for example for NFS attacks or any other protocol relying on addresses for authentification, even when protected from the outside interfaces by firewalling rules. Most of the time, existing firewalling rules are bypassed. This requires at least a shell account on the system. IMPACT Any local user can send any packet to any host from most Linux default installations without of the use of any permission problem or suid flaw. Basically, it corresponds to having write only permissions to raw IP socket on the server machine. IMMUNE CONFIGURATIONS You are immune to this problem if one (or more) of the following is true: - you do not have local (shell) users - SLIP and PPP are not compiled-in the kernel and either are not available in /lib/modules/* as modules, or are never loaded and kerneld/kmod is not available. - you use deny-default configuration for your input firewall rules, and you don't have accept entries for specific addresses or for unused ppp or slip interfaces (and the used ones are never unused or accept rules are safely removed at shutdown). - you use 2.3.18 with ac6 patch (or higher). - you use 2.2.13pre15 (or higher). OPERATING SYSTEMS Linux (any until recently) POSSIBLE-WORK-AROUNDS - Make so that SLIP and PPP support are not available or - Use deny default policy for input firewall, only allow for specific address ranges and specific interfaces. For dynamic links (such as SLIP or PPP), add an accept at link creation time, and remove the entry when the link goes down. FIX - For 2.3.x, install 2.3.18 with the ac6 patch (or higher). Warning, this is a DEVELOPMENT kernel. - For 2.2.x, install 2.2.13pre15 or higher (e.g. 2.2.13). - At this time no fix for 2.0.x. Please apply the above mentionned work-arounds. EXPLOIT Please do not request exploit from the listed authors. Requests for exploits will be ignored. A working exploit exists and has been tested on current Linux distributions. It is possible that an exploit be posted some time in the future (or that someone reads this and does it by himself ...). NOTES This advisory is for information only. No warranty either expressed or implied. Full disclosure and dissemination are allowed as long as this advisory is published in full. No responsability will be taken from abuse or lack of use of the information in this advisory.
This archive was generated by hypermail 2b30 : Fri Apr 13 2001 - 15:08:32 PDT