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Make SSL/TLS version detection less brittle.

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This still cannot deal with v2 hellos that use the long length.
On the other hand - OpenSSL also cannot deal with these and we should
not see many sslv2 connections in any case - so... they probably
would not work in practice in any case.
This commit is contained in:
Bernhard Amann 2014-04-21 11:23:12 -07:00
parent 8ce3cf65f2
commit 594975c93d
2 changed files with 68 additions and 29 deletions
Download patch file Download diff file Expand all files Collapse all files

13
src/analyzer/protocol/ssl/ssl-analyzer.pac
View file

@ -293,6 +293,14 @@ refine connection SSL_Conn += {
return true;
%}
function proc_check_v2_server_hello_version(version: uint16) : bool
%{
if ( version != SSLv20 )
bro_analyzer()->ProtocolViolation(fmt("Invalid version in SSL server hello. Version: %d", version));
return true;
%}
};
#refine typeattr ChangeCipherSpec += &let {
@ -337,6 +345,8 @@ refine typeattr V2ServerHello += &let {
proc : bool = $context.connection.proc_server_hello(rec, server_version, 0,
conn_id_data, 0, 0, ciphers, 0);
check_v2 : bool = $context.connection.proc_check_v2_server_hello_version(server_version);
cert : bool = $context.connection.proc_v2_certificate(rec, cert_data)
&requires(proc);
};
@ -346,8 +356,7 @@ refine typeattr Certificate += &let {
};
refine typeattr V2ClientMasterKey += &let {
proc : bool = $context.connection.proc_v2_client_master_key(rec, cipher_kind)
&requires(state_changed);
proc : bool = $context.connection.proc_v2_client_master_key(rec, cipher_kind);
};
refine typeattr UnknownHandshake += &let {

84
src/analyzer/protocol/ssl/ssl-protocol.pac
View file

@ -36,16 +36,14 @@ type SSLRecord(is_orig: bool) = record {
} &length = length+5, &byteorder=bigendian,
&let {
version : int =
$context.connection.determine_ssl_version(head0, head1, head2);
$context.connection.determine_ssl_record_layer(head0, head1, head2, head3, head4);
content_type : int = case version of {
# UNKNOWN_VERSION -> 0; assume tls on unknown version
SSLv20 -> head2+300;
default -> head0;
};
length : int = case version of {
# UNKNOWN_VERSION -> 0; assume tls on unknown version
SSLv20 -> (((head0 & 0x7f) << 8) | head1) - 3;
default -> (head3 << 8) | head4;
};
@ -277,11 +275,6 @@ type CertificateList = X509Certificate[] &until($input.length() == 0);
type Certificate(rec: SSLRecord) = record {
length : uint24;
certificates : CertificateList &length = to_int()(length);
} &let {
state_changed_client : bool =
$context.connection.startEncryption(true);
state_changed_server : bool =
$context.connection.startEncryption(false);
};
@ -345,6 +338,9 @@ type V2ClientMasterKey(rec: SSLRecord) = record {
key_arg_data : bytestring &length = key_arg_len &transient;
} &length = 7 + cl_key_len + en_key_len + key_arg_len, &let {
cipher_kind : int = (((rec.head3 << 16) | (rec.head4 << 8)) | cipher_kind_8);
# encryption starts for both sides after this message.
state_changed_client : bool = $context.connection.startEncryption(true);
state_changed_server : bool = $context.connection.startEncryption(false);
};
@ -435,41 +431,75 @@ refine connection SSL_Conn += {
%member{
int client_state_;
int server_state_;
int old_state_;
bool hello_requested_;
int record_layer_version_;
%}
%init{
server_state_ = STATE_CLEAR;
client_state_ = STATE_CLEAR;
record_layer_version_ = UNKNOWN_VERSION;
%}
function determine_ssl_version(head0 : uint8, head1 : uint8,
head2 : uint8) : int
function determine_ssl_record_layer(head0 : uint8, head1 : uint8,
head2 : uint8, head3: uint8, head4: uint8) : int
%{
if ( head0 >= 20 && head0 <= 23 &&
head1 == 0x03 && head2 <= 0x03 )
// This is most probably SSL version 3.
return (head1 << 8) | head2;
if ( record_layer_version_ != UNKNOWN_VERSION )
return record_layer_version_;
else if ( head0 >= 128 && head2 < 5 && head2 != 3 )
// Not very strong evidence, but we suspect
// this to be SSLv2.
return SSLv20;
if ( head0 & 0x80 )
{
if ( head2 == 0x01 ) // SSLv2 client hello.
{
uint16 version = (head3<<8) | head4;
if ( version != SSLv20 && version != SSLv30 && version != TLSv10
&& version != TLSv11 && version != TLSv12 )
{
bro_analyzer()->ProtocolViolation(fmt("Invalid version in SSL client hello. Version: %d", version));
return UNKNOWN_VERSION;
}
else
return SSLv20;
}
else
else if ( head2 == 0x04 ) // SSLv2 server hello. This connection will continue using SSLv2.
{
record_layer_version_ = SSLv20;
return SSLv20;
}
else // this is not SSL or TLS.
{
bro_analyzer()->ProtocolViolation(fmt("Invalid headers in SSL connection. Head1: %d, head2: %d, head3: %d", head1, head2, head3));
return UNKNOWN_VERSION;
}
}
uint16 version = (head1<<8) | head2;
if ( version != SSLv30 && version != TLSv10
&& version != TLSv11 && version != TLSv12 )
{
bro_analyzer()->ProtocolViolation(fmt("Invalid version in TLS connection. Version: %d", version));
return UNKNOWN_VERSION;
}
if ( head0 >=20 && head0 <= 30 )
{ // ok, set record layer version, this never can be downgraded to v2
record_layer_version_ = version;
return version;
}
bro_analyzer()->ProtocolViolation(fmt("Invalid type in TLS connection. Version: %d, Type: %d", version, head0));
return UNKNOWN_VERSION;
%}
function client_state() : int %{ return client_state_; %}
function server_state() : int %{ return client_state_; %}
function state(is_orig: bool) : int
%{
if ( is_orig )
return client_state_;
else
return server_state_;
%}
%{
if ( is_orig )
return client_state_;
else
return server_state_;
%}
function startEncryption(is_orig: bool) : bool
%{