CVE-2006-4023 in PHP
Summary
by MITRE
The ip2long function in PHP 5.1.4 and earlier may incorrectly validate an arbitrary string and return a valid network IP address, which allows remote attackers to obtain network information and facilitate other attacks, as demonstrated using SQL injection in the X-FORWARDED-FOR Header in index.php in MiniBB 2.0. NOTE: it could be argued that the ip2long behavior represents a risk for security-relevant issues in a way that is similar to strcpy s role in buffer overflows, in which case this would be a class of implementation bugs that would require separate CVE items for each PHP application that uses ip2long in a security-relevant manner.
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Analysis
by VulDB Data Team • 07/13/2021
The CVE-2006-4023 vulnerability resides in the ip2long function implementation within PHP versions 5.1.4 and earlier, representing a critical security flaw that fundamentally undermines network address validation mechanisms. This vulnerability stems from improper handling of input strings that do not conform to standard IP address formats, allowing the function to return seemingly valid integer representations of invalid network addresses. The flaw manifests when the function processes strings containing non-numeric characters or malformed IP address formats, yet still produces output that appears as legitimate network addresses, creating a dangerous misrepresentation that can be exploited by malicious actors.
The technical implementation of this vulnerability operates through a fundamental flaw in PHP's ip2long function where it fails to properly validate input string formats before converting them to network address integers. When processing strings such as "192.168.1.1abc" or other malformed inputs, the function attempts to parse the numeric portions while ignoring or misinterpreting non-numeric suffixes, resulting in integer values that correspond to valid network address ranges but represent fabricated addresses. This behavior creates a false sense of security for applications that rely on ip2long for input validation, as the function essentially becomes a vector for bypassing security checks that depend on proper IP address validation.
The operational impact of this vulnerability extends beyond simple validation failures, creating significant risks for web applications that process user-supplied IP addresses in security-sensitive contexts. The vulnerability was demonstrated in the MiniBB 2.0 forum software through SQL injection attacks exploiting the X-FORWARDED-FOR header, where attackers could manipulate the ip2long function to generate valid-looking network addresses that bypassed input sanitization measures. This exploitation technique leverages the fact that many applications trust the output of ip2long without additional validation, creating opportunities for attackers to inject malicious data that appears legitimate to network security systems and application logic. The vulnerability essentially creates a pathway for attackers to manipulate network address validation routines and potentially gain unauthorized access to systems or data.
Security implications of CVE-2006-4023 align with CWE-129, which addresses improper validation of array indices and similar input validation flaws that can lead to unauthorized access or data manipulation. The vulnerability demonstrates characteristics similar to buffer overflow risks where improper input handling creates conditions for security-relevant issues, as noted in the CVE description's comparison to strcpy's role in buffer overflows. This classification indicates that the vulnerability represents a fundamental implementation flaw in how PHP handles string-to-integer conversion for network address validation, creating a class of security issues that require application-specific CVE assignments when ip2long is used in security-relevant contexts. Organizations should implement comprehensive input validation measures that independently verify IP address formats before trusting ip2long outputs, particularly in security-sensitive applications that process user-supplied network information.
Mitigation strategies for this vulnerability require immediate patching of affected PHP installations to versions that properly validate input before processing, along with implementing additional validation layers in applications that depend on ip2long functionality. Security teams should conduct comprehensive audits of all applications that utilize ip2long in security-relevant contexts, particularly those handling HTTP headers, user input, or network address validation. The recommended approach includes implementing explicit validation routines that verify the format of input strings before passing them to ip2long, and establishing monitoring protocols to detect anomalous network address patterns that might indicate exploitation attempts. Organizations should also consider implementing web application firewalls that can detect and block suspicious patterns in HTTP headers that might exploit this vulnerability, as the issue primarily manifests through header manipulation rather than direct code injection.