commit ef98d49997bf09f668e2b50cf689535039a48614
author Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> Thu Apr 09 11:56:09 2020 +0200
committer Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> Thu Apr 09 11:56:09 2020 +0200
tree 4bc5f652e23a2006893f500fd8c2afab34e28566
parent 3a1b209f9edaa0b3331b92d8d94b5c60a2ccae5a
parent afbcf97c2051f7f77db58463df4734cc1dd9a866

Merge remote-tracking branch 'restricted/pr/670' into mbedtls-2.16-restricted

* restricted/pr/670:
  Parse HelloVerifyRequest buffer overread: add changelog entry
  Parse HelloVerifyRequest: avoid buffer overread at the start
  Parse HelloVerifyRequest: avoid buffer overread on the cookie

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index 64c72a5..dc2acf7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -8,6 +8,8 @@
      untrusted operating system attacking a secure enclave) to fully recover
      an ECDSA private key. Found and reported by Alejandro Cabrera Aldaya,
      Billy Brumley and Cesar Pereida Garcia. CVE-2020-10932
+   * Fix a potentially remotely exploitable buffer overread in a
+     DTLS client when parsing the Hello Verify Request message.
 
 Bugfix
    * Fix compilation failure when both MBEDTLS_SSL_PROTO_DTLS and

library/ssl_cli.c

diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index afced7a..c5c3af6 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -1417,6 +1417,19 @@
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse hello verify request" ) );
 
+    /* Check that there is enough room for:
+     * - 2 bytes of version
+     * - 1 byte of cookie_len
+     */
+    if( mbedtls_ssl_hs_hdr_len( ssl ) + 3 > ssl->in_msglen )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1,
+            ( "incoming HelloVerifyRequest message is too short" ) );
+        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
+                                    MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
+        return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
+    }
+
     /*
      * struct {
      *   ProtocolVersion server_version;
@@ -1445,8 +1458,6 @@
     }
 
     cookie_len = *p++;
-    MBEDTLS_SSL_DEBUG_BUF( 3, "cookie", p, cookie_len );
-
     if( ( ssl->in_msg + ssl->in_msglen ) - p < cookie_len )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1,
@@ -1455,6 +1466,7 @@
                                     MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
         return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
     }
+    MBEDTLS_SSL_DEBUG_BUF( 3, "cookie", p, cookie_len );
 
     mbedtls_free( ssl->handshake->verify_cookie );