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SSL Analyzer: track connection direction by messages

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This PR changes the way in which the SSL analyzer tracks the direction
of connections. So far, the SSL analyzer assumed that the originator of
a connection would send the client hello (and other associated
client-side events), and that the responder would be the SSL servers.

In some circumstances this is not true, and the initiator of a
connection is the server, with the responder being the client. So far
this confused some of the internal statekeeping logic and could lead to
mis-parsing of extensions.

This reversal of roles can happen in DTLS, if a connection uses STUN -
and potentially in some StartTLS protocols.

This PR tracks the direction of a TLS connection using the hello
request, client hello and server hello handshake messages. Furthermore,
it changes the SSL events from providing is_orig to providing is_client,
where is_client is true for the client_side of a connection. Since the
argument positioning in the event has not changed, old scripts will
continue to work seamlessly - the new semantics are what everyone
writing SSL scripts will have expected in any case.

There is a new event that is raised when a connection is flipped. A
weird is raised if a flip happens repeatedly.

Addresses GH-2198.
This commit is contained in:
Johanna Amann 2022-06-24 19:27:13 +02:00 • committed by Johanna Amann
parent a7aa345c76
commit e14eddeb97
30 changed files with 344 additions and 179 deletions
Download patch file Download diff file Expand all files Collapse all files

102
scripts/base/protocols/ssl/main.zeek
View file

@ -72,9 +72,14 @@ export {
## SSL history showing which types of packets we received in which order.
## Letters have the following meaning with client-sent letters being capitalized:
##
## A direction flip occurs when the client hello packet is not sent from the originator
## of a connection. This can, e.g., occur when DTLS is used in a connection that was
## set up using STUN.
##
## ====== ====================================================
## Letter Meaning
## ====== ====================================================
## ^ direction flipped
## H hello_request
## C client_hello
## S server_hello
@ -198,9 +203,9 @@ function set_session(c: connection)
}
}
function add_to_history(c: connection, is_orig: bool, char: string)
function add_to_history(c: connection, is_client: bool, char: string)
{
if ( is_orig )
if ( is_client )
c$ssl$ssl_history = c$ssl$ssl_history+to_upper(char);
else
c$ssl$ssl_history = c$ssl$ssl_history+to_lower(char);
@ -284,9 +289,9 @@ event ssl_server_hello(c: connection, version: count, record_version: count, pos
c$ssl$resumed = T;
}
event ssl_extension_supported_versions(c: connection, is_orig: bool, versions: index_vec)
event ssl_extension_supported_versions(c: connection, is_client: bool, versions: index_vec)
{
if ( is_orig || |versions| != 1 )
if ( is_client || |versions| != 1 )
return;
set_session(c);
@ -302,20 +307,20 @@ event ssl_ecdh_server_params(c: connection, curve: count, point: string) &priori
c$ssl$curve = ec_curves[curve];
}
event ssl_extension_key_share(c: connection, is_orig: bool, curves: index_vec)
event ssl_extension_key_share(c: connection, is_client: bool, curves: index_vec)
{
if ( is_orig || |curves| != 1 )
if ( is_client || |curves| != 1 )
return;
set_session(c);
c$ssl$curve = ec_curves[curves[0]];
}
event ssl_extension_server_name(c: connection, is_orig: bool, names: string_vec) &priority=5
event ssl_extension_server_name(c: connection, is_client: bool, names: string_vec) &priority=5
{
set_session(c);
if ( is_orig && |names| > 0 )
if ( is_client && |names| > 0 )
{
c$ssl$server_name = names[0];
if ( |names| > 1 )
@ -323,133 +328,140 @@ event ssl_extension_server_name(c: connection, is_orig: bool, names: string_vec)
}
}
event ssl_extension_application_layer_protocol_negotiation(c: connection, is_orig: bool, protocols: string_vec)
event ssl_extension_application_layer_protocol_negotiation(c: connection, is_client: bool, protocols: string_vec)
{
set_session(c);
if ( is_orig )
if ( is_client )
return;
if ( |protocols| > 0 )
c$ssl$next_protocol = protocols[0];
}
event ssl_handshake_message(c: connection, is_orig: bool, msg_type: count, length: count) &priority=5
event ssl_connection_flipped(c: connection)
{
set_session(c);
if ( is_orig && msg_type == SSL::CLIENT_KEY_EXCHANGE )
c$ssl$ssl_history += "^";
}
event ssl_handshake_message(c: connection, is_client: bool, msg_type: count, length: count) &priority=5
{
set_session(c);
if ( is_client && msg_type == SSL::CLIENT_KEY_EXCHANGE )
c$ssl$client_key_exchange_seen = T;
switch ( msg_type )
{
case SSL::HELLO_REQUEST:
add_to_history(c, is_orig, "h");
add_to_history(c, is_client, "h");
break;
case SSL::CLIENT_HELLO:
add_to_history(c, is_orig, "c");
add_to_history(c, is_client, "c");
break;
case SSL::SERVER_HELLO:
add_to_history(c, is_orig, "s");
add_to_history(c, is_client, "s");
break;
case SSL::HELLO_VERIFY_REQUEST:
add_to_history(c, is_orig, "v");
add_to_history(c, is_client, "v");
break;
case SSL::SESSION_TICKET:
add_to_history(c, is_orig, "t");
add_to_history(c, is_client, "t");
break;
# end of early data
case 5:
add_to_history(c, is_orig, "e");
add_to_history(c, is_client, "e");
break;
case SSL::HELLO_RETRY_REQUEST:
add_to_history(c, is_orig, "j");
add_to_history(c, is_client, "j");
break;
case SSL::ENCRYPTED_EXTENSIONS:
add_to_history(c, is_orig, "o");
add_to_history(c, is_client, "o");
break;
case SSL::CERTIFICATE:
add_to_history(c, is_orig, "x");
add_to_history(c, is_client, "x");
break;
case SSL::SERVER_KEY_EXCHANGE:
add_to_history(c, is_orig, "k");
add_to_history(c, is_client, "k");
break;
case SSL::CERTIFICATE_REQUEST:
add_to_history(c, is_orig, "r");
add_to_history(c, is_client, "r");
break;
case SSL::SERVER_HELLO_DONE:
add_to_history(c, is_orig, "n");
add_to_history(c, is_client, "n");
break;
case SSL::CERTIFICATE_VERIFY:
add_to_history(c, is_orig, "y");
add_to_history(c, is_client, "y");
break;
case SSL::CLIENT_KEY_EXCHANGE:
add_to_history(c, is_orig, "g");
add_to_history(c, is_client, "g");
break;
case SSL::FINISHED:
add_to_history(c, is_orig, "f");
add_to_history(c, is_client, "f");
break;
case SSL::CERTIFICATE_URL:
add_to_history(c, is_orig, "w");
add_to_history(c, is_client, "w");
break;
case SSL::CERTIFICATE_STATUS:
add_to_history(c, is_orig, "u");
add_to_history(c, is_client, "u");
break;
case SSL::SUPPLEMENTAL_DATA:
add_to_history(c, is_orig, "a");
add_to_history(c, is_client, "a");
break;
case SSL::KEY_UPDATE:
add_to_history(c, is_orig, "p");
add_to_history(c, is_client, "p");
break;
# message hash
case 254:
add_to_history(c, is_orig, "m");
add_to_history(c, is_client, "m");
break;
default:
add_to_history(c, is_orig, "z");
add_to_history(c, is_client, "z");
break;
}
}
# Extension event is fired _before_ the respective client or server hello.
# Important for client_ticket_empty_session_seen.
event ssl_extension(c: connection, is_orig: bool, code: count, val: string) &priority=5
event ssl_extension(c: connection, is_client: bool, code: count, val: string) &priority=5
{
set_session(c);
if ( is_orig && code == SSL_EXTENSION_SESSIONTICKET_TLS && |val| > 0 )
if ( is_client && code == SSL_EXTENSION_SESSIONTICKET_TLS && |val| > 0 )
# In this case, we might have an empty ID. Set back to F in client_hello event
# if it is not empty after all.
c$ssl$client_ticket_empty_session_seen = T;
else if ( is_orig && code == SSL_EXTENSION_PRE_SHARED_KEY )
else if ( is_client && code == SSL_EXTENSION_PRE_SHARED_KEY )
# In this case, the client sent a PSK extension which can be used for resumption
c$ssl$client_psk_seen = T;
else if ( ! is_orig && code == SSL_EXTENSION_PRE_SHARED_KEY && c$ssl$client_psk_seen )
else if ( ! is_client && code == SSL_EXTENSION_PRE_SHARED_KEY && c$ssl$client_psk_seen )
# In this case, the server accepted the PSK offered by the client.
c$ssl$resumed = T;
}
event ssl_change_cipher_spec(c: connection, is_orig: bool) &priority=5
event ssl_change_cipher_spec(c: connection, is_client: bool) &priority=5
{
set_session(c);
add_to_history(c, is_orig, "i");
add_to_history(c, is_client, "i");
if ( is_orig && c$ssl$client_ticket_empty_session_seen && ! c$ssl$client_key_exchange_seen )
if ( is_client && c$ssl$client_ticket_empty_session_seen && ! c$ssl$client_key_exchange_seen )
c$ssl$resumed = T;
}
event ssl_alert(c: connection, is_orig: bool, level: count, desc: count) &priority=5
event ssl_alert(c: connection, is_client: bool, level: count, desc: count) &priority=5
{
set_session(c);
add_to_history(c, is_orig, "l");
add_to_history(c, is_client, "l");
c$ssl$last_alert = alert_descriptions[desc];
}
event ssl_heartbeat(c: connection, is_orig: bool, length: count, heartbeat_type: count, payload_length: count, payload: string)
event ssl_heartbeat(c: connection, is_client: bool, length: count, heartbeat_type: count, payload_length: count, payload: string)
{
set_session(c);
add_to_history(c, is_orig, "b");
add_to_history(c, is_client, "b");
}
event ssl_established(c: connection) &priority=7
@ -489,7 +501,7 @@ event analyzer_confirmation(c: connection, atype: AllAnalyzers::Tag, aid: count)
}
}
event ssl_plaintext_data(c: connection, is_orig: bool, record_version: count, content_type: count, length: count) &priority=5
event ssl_plaintext_data(c: connection, is_client: bool, record_version: count, content_type: count, length: count) &priority=5
{
set_session(c);