CVE-2006-4467 in Simple Machines
Summary
by MITRE
Simple Machines Forum (SMF) 1.1RCx before 1.1RC3, and 1.0.x before 1.0.8, does not properly unset variables when the input data includes a numeric parameter with a value matching an alphanumeric parameter s hash value, which allows remote attackers to perform directory traversal attacks to read arbitrary local files, lock topics, and possibly have other security impacts. NOTE: it could be argued that this vulnerability is due to a bug in the unset PHP command (CVE-2006-3017) and the proper fix should be in PHP; if so, then this should not be treated as a vulnerability in Simple Machines Forum.
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Analysis
by VulDB Data Team • 08/03/2018
The vulnerability described in CVE-2006-4467 affects Simple Machines Forum versions 1.1RCx before 1.1RC3 and 1.0.x before 1.0.8, representing a critical security flaw that stems from improper variable handling within the forum software's input processing mechanisms. This issue specifically manifests when numeric parameters in input data match the hash values of alphanumeric parameters, creating a condition where variables intended to be unset remain accessible in memory. The flaw exploits PHP's variable handling behavior, particularly the way it processes array keys and hash collisions, which allows attackers to manipulate the forum's internal state through carefully crafted input parameters.
The technical exploitation of this vulnerability occurs through a directory traversal attack vector that leverages PHP's hash collision properties to bypass intended variable unsetting operations. When an attacker submits input containing both numeric and alphanumeric parameters with matching hash values, the forum's code fails to properly unset certain variables that should be cleared after processing. This creates a scenario where attackers can manipulate the forum's internal logic to access arbitrary local files through directory traversal techniques. The vulnerability operates at the intersection of PHP's internal hash table implementation and the forum's input validation routines, making it particularly insidious as it exploits the underlying language mechanics rather than application-specific flaws.
The operational impact of this vulnerability extends beyond simple file reading capabilities to include topic locking functionality and potentially other security implications that could compromise the integrity and availability of the forum. Attackers can leverage this weakness to read sensitive files from the server's filesystem, potentially accessing configuration files, user databases, or other critical system resources. The ability to lock topics represents a denial-of-service capability that could disrupt forum operations and compromise user experience. This vulnerability aligns with CWE-20, "Improper Input Validation," and specifically relates to CWE-254, "Security Features," as it demonstrates how improper handling of input parameters can lead to privilege escalation and unauthorized access. The attack pattern follows techniques described in the ATT&CK framework under T1059 for command and scripting interpreter and T1566 for credential access through exploitation of software vulnerabilities.
The vulnerability's classification as potentially stemming from PHP's own unset function behavior, as referenced in CVE-2006-3017, highlights the complex relationship between application-level security and underlying platform vulnerabilities. This dependency on PHP's internal implementation creates a challenging mitigation landscape where the primary fix should ideally address the root cause in the PHP interpreter itself. However, the forum developers must also implement defensive measures to prevent exploitation while waiting for the underlying PHP fix to be deployed. Organizations should consider implementing input sanitization layers, parameter validation checks, and regular security updates to address this vulnerability. The recommended mitigation strategy includes upgrading to patched versions of Simple Machines Forum, implementing web application firewalls, and conducting thorough input validation to prevent malformed parameters from reaching the vulnerable code paths. Additionally, system administrators should monitor for potential exploitation attempts and maintain comprehensive logging of forum access patterns to detect anomalous behavior that might indicate attempted exploitation of this vulnerability.