> > 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 filesystems > > 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 problem. > 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 battle ultimately. 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 whatnot. Kurt Seifried, [EMAIL PROTECTED] A15B BEE5 B391 B9AD B0EF AEB0 AD63 0B4E AD56 E574 http://seifried.org/security/ ----- Original Message ----- From: "Jeremiah Cornelius" <[EMAIL PROTECTED]> To: "Jakob Lell" <[EMAIL PROTECTED]> Cc: "Steven Leikeim" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> Sent: Wednesday, November 26, 2003 3:18 PM Subject: Re: [Full-Disclosure] Re: hard links on Linux create local DoS vulnerability and security problems > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On Monday 24 November 2003 10:17, Steven Leikeim wrote: > <SNIP> > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.2.3 (GNU/Linux) > > iD8DBQE/xSbQJi2cv3XsiSARAm5CAJwPkETRJxLWAXw3M+B8jjfUwr38aQCeNzU/ > 4AjEdIIdmXmIHA6pYWjb1ao= > =FIsi > -----END PGP SIGNATURE----- > > _______________________________________________ > Full-Disclosure - We believe in it. > Charter: http://lists.netsys.com/full-disclosure-charter.html > _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html
