CVE-2007-3007 in PHP
Summary
by MITRE
PHP 5 before 5.2.3 does not enforce the open_basedir or safe_mode restriction in certain cases, which allows context-dependent attackers to determine the existence of arbitrary files by checking if the readfile function returns a string. NOTE: this issue might also involve the realpath function.
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Analysis
by VulDB Data Team • 07/20/2019
This vulnerability exists in PHP versions prior to 5.2.3 and represents a critical security flaw related to privilege escalation and information disclosure. The issue stems from the improper enforcement of open_basedir and safe_mode restrictions within the PHP runtime environment, which are fundamental security mechanisms designed to limit file access to specific directories and prevent unauthorized file operations. When these restrictions fail to properly validate file access requests, attackers can exploit the weakness to bypass security boundaries and gain unauthorized visibility into the filesystem.
The technical flaw manifests through the readfile function's behavior when processing files outside the designated safe directories. In normal operation, open_basedir should restrict file operations to specific directory paths, while safe_mode should prevent access to files outside the current working directory. However, this vulnerability allows attackers to determine whether specific files exist on the server by observing the return values of the readfile function. When readfile attempts to process a file that exists but is outside the allowed directory boundaries, it returns a string value indicating successful execution, whereas attempting to read a non-existent file results in a different return behavior that attackers can use to map the filesystem structure.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables attackers to perform reconnaissance activities that can lead to more severe exploits. Attackers can systematically test for the existence of sensitive files such as configuration files, database credentials, or application source code by leveraging the predictable return values of readfile. This reconnaissance capability significantly increases the attack surface and can be combined with other vulnerabilities to achieve unauthorized access to sensitive data or system resources. The vulnerability particularly affects web applications that rely on PHP for file operations and do not properly implement additional security measures to compensate for the flawed restriction enforcement.
The implications of this vulnerability align with CWE-276, which addresses improper file permissions and access control mechanisms, and can be categorized under ATT&CK technique T1083 for discovering files and directories. The flaw demonstrates a classic case of privilege escalation through improper access control, where the security boundaries designed to protect the system are circumvented through careful observation of function return values. Organizations running affected PHP versions face significant risks, as this vulnerability can be exploited by remote attackers without requiring special privileges or authentication. The vulnerability also affects the realpath function, which further compounds the security implications by potentially allowing attackers to manipulate file paths and bypass additional security checks that should normally be enforced.
Mitigation strategies for this vulnerability include immediate upgrading to PHP 5.2.3 or later versions where the open_basedir and safe_mode restrictions are properly enforced. System administrators should also implement additional security measures such as proper file permission settings, regular security audits, and monitoring for suspicious file access patterns. Organizations should consider implementing web application firewalls and additional input validation mechanisms to prevent exploitation attempts. The vulnerability underscores the importance of keeping software dependencies updated and maintaining comprehensive security practices that go beyond relying solely on built-in security mechanisms. Regular security assessments and penetration testing can help identify similar vulnerabilities in other components of the web application stack that might provide similar attack vectors for information disclosure and privilege escalation.