From a1098f81c252b317ad34ea978aea2bc47760b215 Mon Sep 17 00:00:00 2001
From: Krzysztof Stachowiak <krzysiek.stachowiak@gmail.com>
Date: Tue, 13 Mar 2018 11:28:49 +0100
Subject: [PATCH 1/3] Add bounds check before signature length read

---
 library/ssl_cli.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 2534346a4..279a127ba 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -2478,6 +2478,14 @@ 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 027f84c69f4ef30c0693832a6c396ef19e563ca1 Mon Sep 17 00:00:00 2001
From: Krzysztof Stachowiak <krzysiek.stachowiak@gmail.com>
Date: Tue, 13 Mar 2018 11:29:24 +0100
Subject: [PATCH 2/3] Prevent arithmetic overflow on bounds 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 279a127ba..df6abc389 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -2489,7 +2489,7 @@ 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 00bbf572afc5558026a65ccb1000023bd1ce872d Mon Sep 17 00:00:00 2001
From: Krzysztof Stachowiak <krzysiek.stachowiak@gmail.com>
Date: Wed, 14 Mar 2018 11:14:13 +0100
Subject: [PATCH 3/3] Update change log

---
 ChangeLog | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index dfd34bf69..6e497bc1d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -17,6 +17,8 @@ Security
      implementation allowed an offline 2^80 brute force attack on the
      HMAC key of a single, uninterrupted connection (with no
      resumption of the session).
+   * Fix a buffer overread in ssl_parse_server_key_exchange() that could cause
+     a crash on invalid input.
 
 Features
    * Extend PKCS#8 interface by introducing support for the entire SHA
@@ -44,6 +46,8 @@ Bugfix
      Nick Wilson on issue #355
    * In test_suite_pk, pass valid parameters when testing for hash length
      overflow. #1179
+   * Fix a possible arithmetic overflow in ssl_parse_server_key_exchange()
+     that could cause a key exchange to fail on valid data.
 
 Changes
    * Fix tag lengths and value ranges in the documentation of CCM encryption.