CVE-2012-6532 in Zend Framework
Summary
by MITRE
(1) Zend_Dom, (2) Zend_Feed, (3) Zend_Soap, and (4) Zend_XmlRpc in Zend Framework 1.x before 1.11.13 and 1.12.x before 1.12.0 allow remote attackers to cause a denial of service (CPU consumption) via recursive or circular references in an XML entity definition in an XML DOCTYPE declaration, aka an XML Entity Expansion (XEE) attack.
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Analysis
by VulDB Data Team • 12/29/2021
The vulnerability identified as CVE-2012-6532 represents a critical denial of service flaw affecting multiple components within the Zend Framework 1.x series. This issue specifically impacts Zend_Dom, Zend_Feed, Zend_Soap, and Zend_XmlRpc modules, which are widely used in enterprise applications for handling XML processing tasks. The vulnerability stems from inadequate input validation mechanisms that fail to properly handle recursive or circular references within XML entity definitions, creating a scenario where malicious actors can exploit XML Entity Expansion techniques to consume excessive CPU resources.
The technical flaw manifests when these framework components process XML documents containing maliciously crafted DOCTYPE declarations with recursive entity references. When the XML parser encounters such constructs, it attempts to resolve the entity references recursively, leading to exponential CPU consumption as the parser follows the circular references indefinitely. This behavior constitutes a classic XML External Entity (XXE) attack vector where the attacker crafts XML content designed to trigger resource exhaustion rather than direct code execution. The vulnerability is particularly dangerous because it affects core XML processing functionality that many applications depend upon for data exchange and web service communication.
The operational impact of this vulnerability extends beyond simple service disruption, as it can effectively render applications unusable by consuming all available CPU resources on the server hosting the vulnerable application. Attackers can trigger this condition with relatively small XML payloads, making the attack efficient and difficult to detect through normal monitoring. The vulnerability affects both the 1.11.x branch prior to version 1.11.13 and the 1.12.x branch prior to version 1.12.0, indicating it was present across multiple release lines of the framework. This widespread impact means that organizations running applications built on Zend Framework 1.x were potentially vulnerable regardless of their specific component usage, as the underlying XML parsing mechanisms remained susceptible to the same exploitation techniques.
Organizations affected by this vulnerability should prioritize immediate patching of their Zend Framework installations to versions 1.11.13 or 1.12.0 respectively, which include proper safeguards against recursive entity resolution. Additionally, implementing XML parser configuration changes that disable external entity resolution and DTD processing can provide additional defense-in-depth measures. Security teams should also consider implementing rate limiting and resource monitoring for XML processing endpoints to detect potential exploitation attempts. This vulnerability aligns with CWE-400, which specifically addresses excessive resource consumption, and maps to ATT&CK technique T1499.004 for resource exhaustion attacks. The issue demonstrates the critical importance of proper input validation in XML processing libraries and highlights the need for robust security practices in enterprise web application frameworks that handle external data inputs.