Date: Wed, 5 Mar 2008 10:19:09 +0100 From: Tomas Hoger <thoger@...hat.com> To: oss-security@...ts.openwall.com Subject: Re: request CVE id: insecure handling of DISPLAY in rxvt On Tue, 4 Mar 2008 22:34:10 +0000 Steve Kemp <steve@...ve.org.uk> wrote: > The idea is that if you typically connect to a host with display > forwarding you'll be used to running rxvt and having the resulting > application display locally. > > However if you forget to enable display forwarding then run > RXVT it will connect to :1, rather than complain there is no > DISPLAY set and abort. That *could* allow a malicious local > server to steal keyboard, & etc. > > However I have a hard time seeing this in practise. It would > mean that locally you couldn't trust root - since it would take > a local root user to setup the fake X11 server on :1.. I don't think you need root privileges to take advantage of this... Let's assume shared box where users ssh -X and run some X programs, e.g. rxvt. Let's assume unprivileged user can start local X session which will be DISPLAY=:0 and do xhost + to allow connections from other users to her display (maybe Xvnc can be used instead of local X session too). Now she just have to wait for some other user to ssh without X forwarding and start rxvt on her display. Yes, many assumptions and ifs, but still silently assuming DISPLAY=:0 when no DISPLAY is set does not sound like a safe default. Just my 2c. -- Tomas Hoger Red Hat Security Response Team
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