Full Disclosure mailing list archives
Re: No shell => secure?
From: "Wall, Kevin" <Kevin.Wall () qwest com>
Date: Fri, 9 Jul 2004 12:30:59 -0500
Matthias Benkmann wrote...
I can't say I've looked at much exploit-code so far but the POC exploits to gain root I've seen for Linux all executed /bin/sh. I'd like to know if this is true for in-the-wild exploits to root a box, too. If so, would it be a useful security measure to rename /bin/sh and other shells (after making sure that everything that needs them has been updated to the new name, of course)?
No; sometimes they use other shells, such as /bin/bash, /bin/ash, /bin/zsh, etc. or else execute a single command at a time. Also, presumably, you'd still have to set SHELL env variable, so they could presumably just execute $SHELL in many cases. Worst of all, you now have yourself a maintenance nightmare. Think of how many shell scripts where you'd have to change the #!/bin/sh to whatever full path name you've switched the shell to. And you'd have to do this whenever you install a vendor update, an RPM, etc. Yuck! No thanks!
I'm aware that a dedicated attacker who targets my box specifically will not be stopped by this but I don't think I have such enemies. I also know that DOS is still possible, but that's also not my concern. I'm simply worried about script kiddies using standard exploits against random servers on the Internet rooting my box faster than I can patch it.
Well, it probably would stop the script kiddies--for awhile at least. But see above. Also, if you keep on top of patches, have appropriate firewall rules and other access control mechanisms in place, script kiddies are not all that hard to keep out.
If renaming the shell is not enough, how about renaming all of the standard Unix top-level directories (such as /bin, /etc,...)? Would that defeat standard exploits to root a box?
Man, that would REALLY become a maintenance nightmare. You'd have to customize almost all RPMs, vendor patches, etc. before installing them. --- -kevin wall Qwest IT - Application Security Team "The reason you have people breaking into your software all over the place is because your software sucks..." -- Former whitehouse cybersecurity advisor, Richard Clarke, at eWeek Security Summit _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html
Current thread:
- Re: No shell => secure?, (continued)
- Re: No shell => secure? Ron DuFresne (Jul 09)
- Re: No shell => secure? Valdis . Kletnieks (Jul 09)
- Re: No shell => secure? Matthias Benkmann (Jul 09)
- Re: No shell => secure? Valdis . Kletnieks (Jul 09)
- Re: No shell => secure? hax (Jul 09)
- Re: No shell => secure? st3ng4h (Jul 09)
- Re: No shell => secure? hax (Jul 09)
- Re: No shell => secure? Matthias Benkmann (Jul 09)
- Re: No shell => secure? Kurt Seifried (Jul 09)
- Re: No shell => secure? Seth Alan Woolley (Jul 12)
- Re: No shell => secure? Wall, Kevin (Jul 09)
- Re: No shell => secure? Martin Fallon (Jul 09)
- RE: No shell => secure? Deckard, Jason (Jul 09)
- Re: No shell => secure? John Creegan (Jul 12)