CVE-2013-4701 in Php-openid
Summary
by MITRE
Auth/Yadis/XML.php in PHP OpenID Library 2.2.2 and earlier allows remote attackers to read arbitrary files, send HTTP requests to intranet servers, or cause a denial of service (CPU and memory consumption) via XRDS data containing an external entity declaration in conjunction with an entity reference, related to an XML External Entity (XXE) issue.
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Analysis
by VulDB Data Team • 01/04/2022
The CVE-2013-4701 vulnerability represents a critical XML External Entity (XXE) flaw within the PHP OpenID Library version 2.2.2 and earlier. This vulnerability specifically affects the Auth/Yadis/XML.php component which processes XRDS (XRDS Document) data during OpenID authentication flows. The flaw arises from insufficient input validation and sanitization of XML content, particularly when handling external entity declarations. Attackers can exploit this weakness by crafting malicious XRDS documents that contain external entity declarations combined with entity references, thereby enabling unauthorized access to system resources and potentially compromising the entire authentication infrastructure.
The technical implementation of this vulnerability stems from the library's failure to properly restrict XML parsing operations, allowing attackers to manipulate the XML parser behavior through carefully constructed XXE payloads. When the vulnerable PHP OpenID library processes XRDS data containing malicious external entity declarations, the XML parser attempts to resolve these entities, leading to multiple attack vectors. The vulnerability enables remote attackers to perform file inclusion attacks against the server hosting the vulnerable application, potentially reading sensitive system files, accessing internal network resources through HTTP requests to intranet servers, or consuming excessive CPU and memory resources to cause denial of service conditions.
From an operational perspective, this vulnerability poses significant risks to web applications implementing OpenID authentication using the affected PHP library. The attack surface extends beyond simple information disclosure to include potential internal network reconnaissance, as attackers can leverage the XXE functionality to send HTTP requests to internal systems that would normally be inaccessible from the internet. The denial of service component of this vulnerability can be particularly damaging in high-traffic environments, where attackers could consume system resources to render services unavailable to legitimate users. This vulnerability directly maps to CWE-611 (Improper Restriction of XML External Entity Reference) and aligns with ATT&CK technique T1213.002 (Data from Information Repositories) and T1499.004 (Application Exhaustion Flood).
Organizations should prioritize immediate remediation by upgrading to PHP OpenID Library version 2.2.3 or later, which includes proper XML parsing restrictions and external entity handling. Additional mitigations include implementing XML parser configurations that disable external entity resolution entirely, deploying web application firewalls with XXE detection capabilities, and conducting thorough security assessments of all OpenID implementations. Network segmentation and access controls should be strengthened to limit potential lateral movement if exploitation occurs. The vulnerability underscores the importance of proper input validation and secure coding practices in XML processing components, particularly in authentication libraries that handle sensitive user data and external communications. Organizations should also implement monitoring and logging for unusual XML parsing activities and ensure regular security updates are applied to all third-party libraries and dependencies.