libxml_disable_entity_loader

libxml_disable_entity_loader is a function in PHP used to disable the ability to load external entities in libxml, which is the library PHP uses for parsing XML. This function is particularly relevant for preventing XML External Entities (XXE) attacks in PHP applications.

The main purpose of libxml_disable_entity_loader is to prevent libxml from loading external entities, which is a common attack vector in XXE attacks. By default, libxml in PHP may load external entities specified in an XML document, which can lead to security vulnerabilities.

A basic example of using it may be:

// Disable the ability to load external entities
libxml_disable_entity_loader(true);

// Load an XML document (without loading any external entities)
$xml = simplexml_load_string($xmlString);

// Re-enable the ability to load external entities if needed
libxml_disable_entity_loader(false);

Before loading an XML string with simplexml_load_string, the loading of external entities is disabled to prevent XXE attacks.

When libxml_disable_entity_loader is set to true, it effectively mitigates the risk of XXE attacks, which can lead to information disclosure, data exfiltration, or server-side request forgery. In PHP 8.0 and newer, libxml_disable_entity_loader has been deprecated, as it no longer affects libxml's entity loader behavior, which is now safe by default. In PHP 7.3 and earlier, where the function isn’t deprecated, it's crucial to use it to secure XML processing.

While libxml_disable_entity_loader helps secure XML processing against XXE attacks, it's also important to ensure that all user-supplied XML data is properly validated and sanitized.