int ssl_check_clienthello_tlsext_early(SSL *s)
	{
	int ret=SSL_TLSEXT_ERR_NOACK;
	int al = SSL_AD_UNRECOGNIZED_NAME;

#ifndef OPENSSL_NO_EC
	/* The handling of the ECPointFormats extension is done elsewhere, namely in 
	 * ssl3_choose_cipher in s3_lib.c.
	 */
	/* The handling of the EllipticCurves extension is done elsewhere, namely in 
	 * ssl3_choose_cipher in s3_lib.c.
	 */
#endif

	if (s->ctx != NULL && s->ctx->tlsext_servername_callback != 0) 
		ret = s->ctx->tlsext_servername_callback(s, &al, s->ctx->tlsext_servername_arg);
	else if (s->initial_ctx != NULL && s->initial_ctx->tlsext_servername_callback != 0) 		
		ret = s->initial_ctx->tlsext_servername_callback(s, &al, s->initial_ctx->tlsext_servername_arg);

#ifdef TLSEXT_TYPE_opaque_prf_input
 	{
		/* This sort of belongs into ssl_prepare_serverhello_tlsext(),
		 * but we might be sending an alert in response to the client hello,
		 * so this has to happen here in
		 * ssl_check_clienthello_tlsext_early(). */

		int r = 1;
	
		if (s->ctx->tlsext_opaque_prf_input_callback != 0)
			{
			r = s->ctx->tlsext_opaque_prf_input_callback(s, NULL, 0, s->ctx->tlsext_opaque_prf_input_callback_arg);
			if (!r)
				{
				ret = SSL_TLSEXT_ERR_ALERT_FATAL;
				al = SSL_AD_INTERNAL_ERROR;
				goto err;
				}
			}

		if (s->s3->server_opaque_prf_input != NULL) /* shouldn't really happen */
			OPENSSL_free(s->s3->server_opaque_prf_input);
		s->s3->server_opaque_prf_input = NULL;

		if (s->tlsext_opaque_prf_input != NULL)
			{
			if (s->s3->client_opaque_prf_input != NULL &&
				s->s3->client_opaque_prf_input_len == s->tlsext_opaque_prf_input_len)
				{
				/* can only use this extension if we have a server opaque PRF input
				 * of the same length as the client opaque PRF input! */

				if (s->tlsext_opaque_prf_input_len == 0)
					s->s3->server_opaque_prf_input = OPENSSL_malloc(1); /* dummy byte just to get non-NULL */
				else
					s->s3->server_opaque_prf_input = BUF_memdup(s->tlsext_opaque_prf_input, s->tlsext_opaque_prf_input_len);
				if (s->s3->server_opaque_prf_input == NULL)
					{
					ret = SSL_TLSEXT_ERR_ALERT_FATAL;
					al = SSL_AD_INTERNAL_ERROR;
					goto err;
					}
				s->s3->server_opaque_prf_input_len = s->tlsext_opaque_prf_input_len;
				}
			}

		if (r == 2 && s->s3->server_opaque_prf_input == NULL)
			{
			/* The callback wants to enforce use of the extension,
			 * but we can't do that with the client opaque PRF input;
			 * abort the handshake.
			 */
			ret = SSL_TLSEXT_ERR_ALERT_FATAL;
			al = SSL_AD_HANDSHAKE_FAILURE;
			}
	}

 err:
#endif
	switch (ret)
		{
		case SSL_TLSEXT_ERR_ALERT_FATAL:
			ssl3_send_alert(s,SSL3_AL_FATAL,al); 
			return -1;

		case SSL_TLSEXT_ERR_ALERT_WARNING:
			ssl3_send_alert(s,SSL3_AL_WARNING,al);
			return 1; 
					
		case SSL_TLSEXT_ERR_NOACK:
			s->servername_done=0;
			default:
		return 1;
		}
	}

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.