CVE-2014-1439 in HipHop Virtual Machine for PHP
Summary
by MITRE
The libxml_disable_entity_loader function in runtime/ext/ext_simplexml.cpp in HipHop Virtual Machine for PHP (HHVM) before 2.4.0 and 2.3.x before 2.3.3 does not properly disable a certain libxml handler, which allows remote attackers to conduct XML External Entity (XXE) attacks.
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Analysis
by VulDB Data Team • 02/01/2022
The vulnerability described in CVE-2014-1439 represents a critical security flaw in the HipHop Virtual Machine implementation of PHP's SimpleXML extension. This issue affects HHVM versions prior to 2.4.0 and 2.3.x versions before 2.3.3, where the libxml_disable_entity_loader function fails to properly disable a specific libxml handler. The flaw enables remote attackers to exploit XML External Entity vulnerabilities by manipulating how external entities are processed during XML parsing operations.
The technical root cause of this vulnerability stems from an incomplete implementation of the libxml_disable_entity_loader function within HHVM's runtime environment. When this function is called, it should prevent the loading of external entities in XML documents to mitigate XXE attack vectors. However, the implementation in affected HHVM versions leaves certain libxml handlers active, allowing attackers to bypass the intended security restrictions. This partial disablement creates a pathway for malicious XML content to reference external resources, potentially leading to information disclosure, denial of service, or even remote code execution depending on the system configuration.
From an operational perspective, this vulnerability poses significant risks to web applications that process untrusted XML input through HHVM. Attackers can craft malicious XML documents that reference external entities, potentially accessing internal system resources, conducting server-side request forgery attacks, or retrieving sensitive data from the application server. The impact extends beyond simple data leakage as the vulnerability can be leveraged in combination with other attack vectors to escalate privileges or compromise entire application environments. Organizations using HHVM for PHP applications must consider this vulnerability as a critical threat requiring immediate attention.
The vulnerability aligns with CWE-611, which specifically addresses Improper Restriction of XML External Entity Reference, and maps to ATT&CK technique T1213.002 for Data from Information Repositories. Organizations should implement immediate mitigations including upgrading to patched HHVM versions, implementing proper input validation for XML content, and configuring web application firewalls to detect and block suspicious XML patterns. Additionally, application developers should avoid using vulnerable XML parsing functions and implement proper entity loading restrictions even when relying on third-party libraries. The security community should monitor for similar implementations in other PHP environments and ensure that all XML processing components properly disable external entity loading to prevent similar vulnerabilities from emerging in other systems.