Date: Пт, 22 окт 1999 12:34:33
От: Marc SCHAEFER <schaefer@ALPHANET.CH>
Кому: BUGTRAQ@SECURITYFOCUS.COM
Тема: Local user can send forged packets
--------------------------------------------------------------------------------
NAME
user-rawip-attack
AUTHOR
Marc SCHAEFER <schaefer@alphanet.ch>
with the help of Alan COX (for the fix)
and of Andreas Trottmann <andreas.trottmann@werft22.com> 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.
