CVE-2006-5706 in PHP
Summary
by MITRE
Unspecified vulnerabilities in PHP, probably before 5.2.0, allow local users to bypass open_basedir restrictions and perform unspecified actions via unspecified vectors involving the (1) chdir and (2) tempnam functions. NOTE: the tempnam vector might overlap CVE-2006-1494.
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Analysis
by VulDB Data Team • 04/26/2026
The vulnerability described in CVE-2006-5706 represents a critical security flaw in PHP versions prior to 5.2.0 that allows local attackers to circumvent important security restrictions. This issue specifically targets the open_basedir directive, which is a fundamental PHP security mechanism designed to limit file access to specific directories and prevent unauthorized file operations. The vulnerability manifests through two primary functions: chdir and tempnam, both of which are commonly used in web applications for directory navigation and temporary file creation respectively.
The technical flaw exploited in this vulnerability stems from improper validation of directory paths within the PHP runtime environment. When the chdir function is used, it can potentially allow attackers to traverse directories beyond the intended boundaries set by open_basedir restrictions. Similarly, the tempnam function, which creates temporary files in designated directories, may not properly enforce the directory limitations imposed by open_basedir. This creates a scenario where local users can bypass these security controls through crafted input or specific execution conditions that manipulate how these functions handle path resolution and validation.
The operational impact of this vulnerability is significant for any system running affected PHP versions, particularly web servers hosting multiple applications or users. Attackers could potentially access files outside the designated web root directories, read sensitive information, execute arbitrary code, or perform other malicious actions that would normally be prevented by the open_basedir restrictions. The overlap with CVE-2006-1494 suggests that the tempnam function vector might share similar underlying causes, indicating a broader pattern of path handling issues within PHP's file operation functions. This vulnerability directly violates the principle of least privilege and could enable privilege escalation or information disclosure attacks.
The security implications extend beyond simple file access violations, as this vulnerability could be leveraged to compromise entire web server environments. Systems using PHP with open_basedir configured for security purposes would effectively lose their protection when these functions are exploited. The vulnerability aligns with CWE-22 (Improper Limiting of a Pathname to a Restricted Directory) and CWE-73 (External Control of File Name or Path) categories, representing classic path traversal and privilege escalation risks. From an ATT&CK framework perspective, this vulnerability maps to T1059 (Command and Scripting Interpreter) and T1566 (Phishing) techniques, as attackers could use it to execute malicious code or gain unauthorized access to sensitive files. Organizations should immediately upgrade to PHP 5.2.0 or later versions, implement proper input validation, and review all applications using these functions to ensure no exploitation paths remain available.
This vulnerability demonstrates the critical importance of proper input validation and path handling in web applications. The issue highlights how seemingly innocuous functions like chdir and tempnam can become attack vectors when not properly secured against malicious input. The overlap with CVE-2006-1494 indicates that this was part of a broader class of vulnerabilities affecting PHP's file handling mechanisms, emphasizing the need for comprehensive security reviews of core language functions. Legacy systems running affected PHP versions pose significant risks and require immediate remediation to prevent potential exploitation by threat actors.