CVE-2005-3389 in PHP
Summary
by MITRE
The parse_str function in PHP 4.x up to 4.4.0 and 5.x up to 5.0.5, when called with only one parameter, allows remote attackers to enable the register_globals directive via inputs that cause a request to be terminated due to the memory_limit setting, which causes PHP to set an internal flag that enables register_globals and allows attackers to exploit vulnerabilities in PHP applications that would otherwise be protected.
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Analysis
by VulDB Data Team • 06/11/2019
The vulnerability described in CVE-2005-3389 represents a critical security flaw in PHP's parse_str function that existed across multiple versions including PHP 4.x up to 4.4.0 and 5.x up to 5.0.5. This issue stems from how PHP handles memory management and internal flag setting when processing certain input parameters. The vulnerability specifically manifests when the parse_str function is invoked with only a single parameter, creating a scenario where remote attackers can manipulate the application's behavior through carefully crafted inputs that trigger memory limit exhaustion. The technical mechanism involves the PHP interpreter's internal state management where memory limit violations cause the system to set an internal flag that inadvertently enables the register_globals directive, a feature that was historically considered dangerous due to its potential for security exploitation.
The operational impact of this vulnerability is severe as it fundamentally undermines the security model of PHP applications by allowing attackers to bypass normal input validation and sanitization mechanisms. When register_globals is enabled, variables from external sources such as GET, POST, and COOKIE data automatically become available as global variables within the PHP script's scope, creating numerous attack vectors for exploitation. This flaw directly relates to CWE-121, which addresses buffer overflow conditions, and CWE-122, concerning buffer overflow in heap memory, as the vulnerability exploits memory management behaviors to achieve unintended state changes. The attack surface expands significantly because applications that previously relied on proper input handling and variable scope management can suddenly become vulnerable to parameter manipulation attacks, especially in environments where register_globals was disabled but the internal flag mechanism could still be triggered.
The exploitability of this vulnerability is enhanced by the fact that it leverages legitimate PHP memory management behaviors rather than requiring complex injection techniques. Attackers can craft inputs that cause the parse_str function to consume excessive memory, triggering the memory limit termination and subsequently enabling register_globals. This creates a situation where the vulnerability can be exploited without requiring direct access to the server configuration or knowledge of specific application internals. The attack pattern aligns with ATT&CK technique T1190, which involves exploiting vulnerabilities in software to gain unauthorized access, and T1068, focusing on exploiting vulnerabilities in operating systems or applications. The flaw essentially creates a bypass mechanism that allows attackers to circumvent security controls that would normally prevent parameter manipulation, making it particularly dangerous for applications that depend on proper variable isolation and input validation for their security posture.
The recommended mitigations for this vulnerability involve immediate patching of affected PHP versions to the latest stable releases where the issue has been resolved. Organizations should also implement strict input validation and sanitization practices to prevent malicious inputs from reaching vulnerable functions. Additionally, the register_globals directive should be disabled in all PHP configurations as a defensive measure, even though the vulnerability specifically exploits a scenario where this setting might be inadvertently enabled. Security monitoring should be enhanced to detect unusual memory consumption patterns that might indicate exploitation attempts, and application firewalls or intrusion detection systems should be configured to block suspicious parameter combinations that could trigger the vulnerability conditions. The fundamental solution requires updating PHP installations to versions that properly handle memory limit violations without setting unintended internal flags that could compromise security controls.