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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

1
scripts/base/protocols/ssl/files.zeek
View file

@ -152,6 +152,7 @@ event file_sniff(f: fa_file, meta: fa_metadata) &priority=5
c$ssl$client_cert_chain_fps = string_vec();
}
# Note - for SSL connections, is_orig indicates client/server, not necessary originator/responder.
if ( f$is_orig )
c$ssl$client_cert_chain += f$info;
else

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);