Commit c2c49969 authored by Dr. Stephen Henson's avatar Dr. Stephen Henson
Browse files

Allow renegotiation if SSL_OP_LEGACY_SERVER_CONNECT is set as well as 

initial connection to unpatched servers. There are no additional security
concerns in doing this as clients don't see renegotiation during an
attack anyway.
parent 47e0a1c3

CHANGES

+1 −1
Original line number Diff line number Diff line
@@ -926,7 +926,7 @@ 
     [Steve Henson]



  *) Add option SSL_OP_LEGACY_SERVER_CONNECT which will allow clients to

     connect (but not renegotiate) with servers which do not support RI.

     connect and renegotiate with servers which do not support RI.

     Until RI is more widely deployed this option is enabled by default.

     [Steve Henson]

doc/ssl/SSL_CTX_set_options.pod

+12 −9
Original line number Diff line number Diff line
@@ -237,7 +237,7 @@ OpenSSL 0.9.8m and later always attempts to use secure renegotiation as 
described in RFC5746. This counters the prefix attack described in

CVE-2009-3555 and elsewhere.



The deprecated and highly broken SSLv2 protocol does not support secure

The deprecated and highly broken SSLv2 protocol does not support

renegotiation at all: its use is B<strongly> discouraged.



This attack has far reaching consequences which application writers should be
@@ -276,10 +276,14 @@ was refused. 
=head2 Patched OpenSSL client and unpatched server.



If the option B<SSL_OP_LEGACY_SERVER_CONNECT> is set then initial connections

between patched OpenSSL clients and unpatched servers succeed. This option

is currently set by default even though it has security implications: otherwise

it would be impossible to connect to unpatched servers (i.e. all of them

initially) and this is clearly not acceptable.

and renegotiation between patched OpenSSL clients and unpatched servers

succeeds.



This option is currently set by default even though it has security

implications: otherwise it would be impossible to connect to unpatched servers

(i.e. all of them initially) and this is clearly not acceptable. Renegotiation

is permitted because this does not add any additional security issues: during

an attack clients do not see any renegotiations anyway.



As more servers become patched the option B<SSL_OP_LEGACY_SERVER_CONNECT> will

B<not> be set by default in a future version of OpenSSL.
@@ -292,10 +296,9 @@ unpatched servers (and thus avoid any security issues) should always B<clear> 
B<SSL_OP_LEGACY_SERVER_CONNECT> using SSL_CTX_clear_options() or

SSL_clear_options().



Renegotiation between a patched OpenSSL client and unpatched server follows

the same scheme as between an unpatched client and a patched OpenSSL server:

i.e. it is not permitted unless the option

B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set.

As in the previous case if the option

B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then renegotiation

B<always> succeeds.



=head1 RETURN VALUES

ssl/t1_lib.c

+2 −2
Original line number Diff line number Diff line
@@ -1157,8 +1157,8 @@ int ssl_parse_serverhello_tlsext(SSL *s, unsigned char **p, unsigned char *d, in 
	 * which doesn't support RI so for the immediate future tolerate RI

	 * absence on initial connect only.

	 */

	if (!renegotiate_seen && 

		(s->new_session || !(s->options & SSL_OP_LEGACY_SERVER_CONNECT))

	if (!renegotiate_seen

		&& !(s->options & SSL_OP_LEGACY_SERVER_CONNECT)

		&& !(s->options & SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION))

		{

		*al = SSL_AD_HANDSHAKE_FAILURE;