CVE-2006-3017 in PHP
Summary
by MITRE
zend_hash_del_key_or_index in zend_hash.c in PHP before 4.4.3 and 5.x before 5.1.3 can cause zend_hash_del to delete the wrong element, which prevents a variable from being unset even when the PHP unset function is called, which might cause the variable s value to be used in security-relevant operations.
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Analysis
by VulDB Data Team • 06/23/2019
The vulnerability described in CVE-2006-3017 represents a critical hash table manipulation flaw within the PHP scripting language implementation that affects versions prior to 4.4.3 and 5.1.3. This issue resides in the zend_hash_del_key_or_index function located in zend_hash.c, which is part of PHP's internal hash table management system. The flaw specifically manifests when the zend_hash_del function attempts to remove elements from hash tables, causing incorrect element deletion behavior that directly impacts variable unsetting operations.
The technical nature of this vulnerability stems from improper handling of hash table operations where the deletion mechanism fails to correctly identify and remove the intended element from the hash structure. When PHP's unset function is invoked on a variable, the underlying hash table management should properly locate and remove that specific element. However, due to the flawed implementation in zend_hash_del_key_or_index, the system may delete a different element from the hash table than the one referenced by the unset operation. This misbehavior creates a scenario where variables appear to be unset but remain accessible in memory, effectively bypassing PHP's variable scoping and cleanup mechanisms.
The operational impact of this vulnerability extends beyond simple variable management issues and presents significant security implications for applications relying on proper variable unsetting for security controls. When variables cannot be properly unset, their values may persist in memory and potentially be accessed by subsequent operations or code sections. This persistence can lead to information disclosure scenarios where sensitive data remains accessible beyond its intended scope, or more critically, allows for potential exploitation of variables containing authentication tokens, session identifiers, or other security-relevant information. The vulnerability directly contradicts the fundamental security principle that unset variables should be completely removed from memory and inaccessible to subsequent operations.
This vulnerability aligns with CWE-254, which addresses weaknesses in the implementation of security features, specifically focusing on improper handling of security-relevant data. The flaw also relates to ATT&CK technique T1059, which involves the execution of malicious code through scripting languages, as the improper variable handling could enable attackers to manipulate application state or access sensitive data. The security implications become particularly severe in web applications where PHP manages user sessions, handles authentication tokens, or processes sensitive user input, as the persistence of unset variables could lead to session hijacking, privilege escalation, or data leakage scenarios. The vulnerability demonstrates how low-level implementation flaws in core language components can create widespread security issues across applications built on that platform.
Organizations should immediately upgrade to PHP versions 4.4.3 or 5.1.3 and later to address this vulnerability. Additionally, application developers should conduct thorough code reviews to identify any potential dependencies on variables that might not be properly unset, and implement defensive programming practices to minimize the impact of such vulnerabilities. System administrators should monitor for any unusual memory patterns or data access behaviors that might indicate exploitation attempts. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date software components and the potential for seemingly minor implementation flaws to create significant security risks in web applications.