From b3e8f9e2e6d6ac4314d8a8a754e684f5bdae7183 Mon Sep 17 00:00:00 2001 From: Krzysztof Stachowiak Date: Wed, 14 Mar 2018 11:40:55 +0100 Subject: [PATCH 1/3] Add bounds check before signature --- library/ssl_cli.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/library/ssl_cli.c b/library/ssl_cli.c index 2534346a49..54a290c4e5 100644 --- a/library/ssl_cli.c +++ b/library/ssl_cli.c @@ -2478,6 +2478,13 @@ static int ssl_parse_server_key_exchange( mbedtls_ssl_context *ssl ) /* * Read signature */ + if( p > end - 2 ) + { + MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) ); + mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL, + MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR ); + return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE ); + } sig_len = ( p[0] << 8 ) | p[1]; p += 2; From b5609f3ca55628f6b88ddc863569cf54ce383471 Mon Sep 17 00:00:00 2001 From: Krzysztof Stachowiak Date: Wed, 14 Mar 2018 11:41:47 +0100 Subject: [PATCH 2/3] Prevent arithmetic overflow on bould check --- library/ssl_cli.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/library/ssl_cli.c b/library/ssl_cli.c index 54a290c4e5..2eec7665b1 100644 --- a/library/ssl_cli.c +++ b/library/ssl_cli.c @@ -2488,7 +2488,7 @@ static int ssl_parse_server_key_exchange( mbedtls_ssl_context *ssl ) sig_len = ( p[0] << 8 ) | p[1]; p += 2; - if( end != p + sig_len ) + if( p != end - sig_len ) { MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) ); mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL, From 4e0141fc00165d12db4453c9b3baa461cf96a4a2 Mon Sep 17 00:00:00 2001 From: Krzysztof Stachowiak Date: Wed, 14 Mar 2018 11:43:00 +0100 Subject: [PATCH 3/3] Update change log --- ChangeLog | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/ChangeLog b/ChangeLog index 8db0215914..cc550fc86d 100644 --- a/ChangeLog +++ b/ChangeLog @@ -46,6 +46,8 @@ Security * Change default choice of DHE parameters from untrustworthy RFC 5114 to RFC 3526 containing parameters generated in a nothing-up-my-sleeve manner. + * Fix a buffer overread in ssl_parse_server_key_exchange() that could cause + a crash on invalid input. Features * Allow comments in test data files. @@ -180,6 +182,8 @@ Bugfix * In mbedtls_entropy_free(), properly free the message digest context. * Fix status handshake status message in programs/ssl/dtls_client.c. Found and fixed by muddog. + * Fix a possible arithmetic overflow in ssl_parse_server_key_exchange() + that could cause a key exchange to fail on valid data. Changes * Extend cert_write example program by options to set the certificate version