[Full-Disclosure] Re: hard links on Linux create local DoS vulnerability and security problems
listuser at seifried.org
Wed Nov 26 23:47:02 GMT 2003
> > There is a simpler solution. Place user files on a separate filesystem
> > from system files. This includes putting all temporary files on separate
> > filesystems of their own. (Both /tmp and /var/tmp.) Since hard links
> > cannot cross filesystems the problem disappears. Mounting user
> > nosuid and nodev will prevent security problems should a setuid binary
> > appear in that filesystem.
See, this is semi intelligent. any user writeable filesystem, typically
/tmp, /var/tmp, /home and sem-writeable fs's like /var/spool/mail (everyone
forgets the mail spool), mail queues, etc, etc will largely solve this
> And a mandatory system profile in /etc , which aliases ln as 'ln -s' might
> help. One for each valid shell.
That is without a doubt one of the silliest things I have heard.
1) hard links are legitimate, very useful (think chroot)
2) alias'ing a commands... *snicker*. So I copy the ln binary to another
name and execute it (which causes you to make /home, /tmp, etc noexec, to
which the attacker replies with "/lib/ld-linux.so.2 /tmp/my-ln", a losing
3) change my shell, unalias the command, etc.
My advice: learn to use the "find" command to look for files and directories
that are writeable by users (either world writeable, writeable by groups the
users belong to, or owned by the user themself) and move those directories
onto seperate partitions. Forgot the silliness of playing with "alias" and
Kurt Seifried, kurt at seifried.org
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----- Original Message -----
From: "Jeremiah Cornelius" <jeremiah at nur.net>
To: "Jakob Lell" <jlell at JakobLell.de>
Cc: "Steven Leikeim" <steven at enel.ucalgary.ca>;
<full-disclosure at lists.netsys.com>; <bugtraq at securityfocus.com>
Sent: Wednesday, November 26, 2003 3:18 PM
Subject: Re: [Full-Disclosure] Re: hard links on Linux create local DoS
vulnerability and security problems
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> On Monday 24 November 2003 10:17, Steven Leikeim wrote:
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