bugtraq - Re: Re: hard links on Linux create local DoS vulnerability and security problems

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <004501c3b477$97846510$1400000a@bigdog>
Date: Wed, 26 Nov 2003 16:47:02 -0700
From: "Kurt Seifried" <listuser@...fried.org>
To: "Jeremiah Cornelius" <jeremiah@....net>, "Jakob Lell" <jlell@...obLell.de>
Cc: "Steven Leikeim" <steven@...l.ucalgary.ca>,
   <full-disclosure@...ts.netsys.com>, <bugtraq@...urityfocus.com>
Subject: Re: Re: hard links on Linux create local DoS vulnerability and security problems

> > 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, kurt@...fried.org
A15B BEE5 B391 B9AD B0EF
AEB0 AD63 0B4E AD56 E574
http://seifried.org/security/

----- Original Message ----- 
From: "Jeremiah Cornelius" <jeremiah@....net>
To: "Jakob Lell" <jlell@...obLell.de>
Cc: "Steven Leikeim" <steven@...l.ucalgary.ca>;
<full-disclosure@...ts.netsys.com>; <bugtraq@...urityfocus.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

> -----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