libxml_disable_entity_loader()

(PHP 5 >= 5.2.11, PHP 7)

Disable the ability to load external entities

说明

libxml_disable_entity_loader([bool $disable= TRUE]): bool

Disable/enable the ability to load external entities.

参数

$disable: Disable(TRUE)or enable(FALSE)libxml extensions(such as DOM,XMLWriter and XMLReader)to load external entities.

返回值

Returns the previous value.

参见

libxml_use_internal_errors()Disable libxml errors and allow user to fetch error information as needed
The LIBXML_NONET constant

If is called 
libxml_disable_entity_loader(true);
, it causes that new SoapClient(.) fails with
SOAP-ERROR: Parsing WSDL: Couldn't load from 'D:\path/dm_operations.wsdl' : failed to load external entity "D:\path/dm_operations.wsdl
because this wsdl imports a xsd as an another external file.
Tested on php 7.1.12, win x64.

Using this function you can prevent a vulnerable to Local and Remote File Inclusion attacks.
You'll see it in an example where I load and validate the following string:
<!DOCTYPE scan [<!ENTITY test SYSTEM "php://filter/read=convert.base64-encode/resource=/etc/passwd">]>
<scan>&test;</scan>
One way to prevent that the file in given back is to set this value to 0.
Please take a closer look at the release of symfony 2.0.11

Be mindful that this also disables url loading in simplexml_load_file() and likely other libxml based functions that deal with URLs

This also seems to have an impact on <xsl:import /> statements if this is applied when loading XSLT for the XSLTProcessor class.

This function was reported to be not thread safe. So this might affect php-scripts on the same server.