SSLv2-support NSE Script

["kkappel () gmail com" <kkappel () gmail com>]

I've noticed the SSLv2-support.nse script included in the Nmap
4.21ALPHA4download doesn't check SSL running on uncommon ports if the
service scan
comes back as "ssl", instead of "ssl/http".  This is common when ssl is used
to secure apps other than http...such as IMAPs (993) or SMTPs (465).  I
updated the script and pasted it below.

(All credit goes to the original author, Matt <mb2263 () bristol ac uk>)


id = "SSLv2"
description = "determines whether the server (still) supports SSL-v2, and
what cyphers it offers."
author = "Matt <mb2263 () bristol ac uk>"
license = "See nmaps COPYING for licence"

categories = {"intrusive"}

portrule = function(host, port)
    if     (    port.number == 443
        or    port.service == "ssl/http"
        or    port.service == "ssl"
        or    port.service == "https")
        and port.protocol == "tcp"
        and port.state == "open"
    then
        return true
    else
        return false
    end

end

hex2dec = function(hex)

    local byte1, byte2;

    byte1 = string.byte(hex, 1);
    byte2 = string.byte(hex, 2);

    if (byte1 == nil or byte2 == nil) then return 0; end;

    return (byte1 * 256) + byte2;

end

cyphers = function(cypher_list, len)

-- returns names of cyphers supported by the server

    local cypher;
    local cypher_name;
    local byte1, byte2, byte3;
    local available_cyphers = "";
    local idx = 0;

    local ssl_cyphers = {
-- (cut down) table of codes with their corresponding cyphers.
-- stolen from wireshark's 'epan/dissectors/packet-ssl-utils.h'
        [0x010080] = "SSL2_RC4_128_WITH_MD5",
        [0x020080] = "SSL2_RC4_128_EXPORT40_WITH_MD5",
        [0x030080] = "SSL2_RC2_CBC_128_CBC_WITH_MD5",
        [0x040080] = "SSL2_RC2_CBC_128_CBC_WITH_MD5",
        [0x050080] = "SSL2_IDEA_128_CBC_WITH_MD5",
        [0x060040] = "SSL2_DES_64_CBC_WITH_MD5",
        [0x0700c0] = "SSL2_DES_192_EDE3_CBC_WITH_MD5",
        [0x080080] = "SSL2_RC4_64_WITH_MD5",
    };

    if (len == 0) then return "\tthe server didn't offer any cyphers"; end
-- something's got broken along the way if these aren't equal
    if (len ~= string.len(cypher_list)) then
        return "";
    end

    for idx = 1, len, 3 do
        cypher = string.sub(cypher_list, idx, idx + 2);

        byte1 = string.byte(cypher, 1);
        byte2 = string.byte(cypher, 2);
        byte3 = string.byte(cypher, 3);

        cypher = (byte1 * 256 * 256) + (byte2 * 256) + byte3;

        cypher_name = ssl_cyphers[cypher];

        if (cypher_name == nil) then
            cypher_name = "unknown cypher (" .. byte1 .. "-" .. byte2 .. "-"
.. byte3 .. " dec)"
        end

        available_cyphers = available_cyphers .. "\t" .. cypher_name ..
"\n";

    end

    return available_cyphers

end

give_n_bytes = function(idx, n, str)

-- returns the next n bytes of a string

    if (idx + (n - 1) > string.len(str)) then
        return (idx + n), string.rep(string.char(0x00), n);
    end

    return (idx + n), string.sub(str, idx, (idx + (n - 1)) );

end

action = function(host, port)

    local socket = nmap.new_socket();
    local status = true;

    local tmp;

    local idx = 3;    -- start reading after the end of the length record

    local return_string = "";
    local available_cyphers = "";

    local ssl_v2_hello;
    local server_hello;

    local server_hello_len;
    local message_type;
    local SID_hit;
    local certificate_type;
    local ssl_version;
    local certificate_len;
    local cyphers_len;
    local certificate;
    local connection_ID_len;
    local cypher_list;
    local connection_ID;

-- build client hello packet (contents stolen from
-- 
http://mail.nessus.org/pipermail/plugins-writers/2004-October/msg00041.html)
    local t = {};
    table.insert(t, string.char(0x80, 0x31));
    table.insert(t, string.char(0x01));
    table.insert(t, string.char(0x00, 0x02));
    table.insert(t, string.char(0x00, 0x18));
    table.insert(t, string.char(0x00, 0x00));
    table.insert(t, string.char(0x00, 0x10));
    table.insert(t, string.char(0x07, 0x00, 0xc0));
    table.insert(t, string.char(0x05, 0x00, 0x80));
    table.insert(t, string.char(0x03, 0x00, 0x80));
    table.insert(t, string.char(0x01, 0x00, 0x80));
    table.insert(t, string.char(0x08, 0x00, 0x80));
    table.insert(t, string.char(0x06, 0x00, 0x40));
    table.insert(t, string.char(0x04, 0x00, 0x80));
    table.insert(t, string.char(0x02, 0x00, 0x80));
    table.insert(t, string.char(0xe4, 0xbd, 0x00, 0x00));
    table.insert(t, string.char(0xa4, 0x41, 0xb6, 0x74));
    table.insert(t, string.char(0x71, 0x2b, 0x27, 0x95));
    table.insert(t, string.char(0x44, 0xc0, 0x3d, 0xc0));
    ssl_v2_hello = table.concat(t, "")

    socket:connect(host.ip, port.number, "tcp");
    socket:send(ssl_v2_hello);

    status, server_hello = socket:receive_bytes(2);

    if (not status) then
        socket:close();
        return;
    end

    server_hello_len = string.sub(server_hello, 1, 2);
    server_hello_len = hex2dec(server_hello_len);
-- length record doesn't include its own length, and is "broken".
    server_hello_len = server_hello_len - (128 * 256) + 2;

-- the hello needs to be at least 13 bytes long to be of any use
    if (server_hello_len < 13) then
        socket:close();
        return;
    end
--try to get entire hello, if we don't already
    if (string.len(server_hello) < server_hello_len) then
        status, tmp = socket:receive_bytes(server_hello_len - string.len
(server_hello));

        if (not status) then
            socket:close();
            return;
        end

        server_hello = server_hello .. tmp;
    end;

    socket:close();

-- split up server hello into components
    idx, message_type =     give_n_bytes(idx, 1, server_hello);
    idx, SID_hit =             give_n_bytes(idx, 1, server_hello);
    idx, certificate_type =     give_n_bytes(idx, 1, server_hello);
    idx, ssl_version =         give_n_bytes(idx, 2, server_hello);
    idx, certificate_len =         give_n_bytes(idx, 2, server_hello);
        certificate_len = hex2dec(certificate_len);
    idx, cyphers_len =         give_n_bytes(idx, 2, server_hello);
        cyphers_len = hex2dec(cyphers_len);
    idx, connection_ID_len =     give_n_bytes(idx, 2, server_hello);
        connection_ID_len = hex2dec(connection_ID_len);
    idx, certificate =         give_n_bytes(idx, certificate_len,
server_hello);
    idx, cypher_list =         give_n_bytes(idx, cyphers_len, server_hello);
    idx, connection_ID =         give_n_bytes(idx, connection_ID_len,
server_hello);

-- some sanity checks:
-- is response a server hello?
    if (message_type ~= string.char(0x04)) then
        return;
    end
-- is certificate in X.509 format?
    if (certificate_type ~= string.char(0x01)) then
        return;
    end

-- actually run some tests:
    if (ssl_version == string.char(0x00, 0x02)) then
        return_string = "server still supports SSLv2\n";
    end

    available_cyphers = cyphers(cypher_list, cyphers_len);

    if (    string.len(return_string) > 0
    or    string.len(available_cyphers) > 0) then
            return return_string .. available_cyphers;
    else
            return;
    end

end

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