Parse HelloVerifyRequest: avoid buffer overread at the start
In ssl_parse_hello_verify_request, we read 3 bytes (version and cookie
length) without checking that there are that many bytes left in
ssl->in_msg. This could potentially read from memory outside of the
ssl->receive buffer (which would be a remotely exploitable
crash).
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index eeedfe6..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;