CVE-2008-2665 in PHP
Summary
by MITRE
Directory traversal vulnerability in the posix_access function in PHP 5.2.6 and earlier allows remote attackers to bypass safe_mode restrictions via a .. (dot dot) in an http URL, which results in the URL being canonicalized to a local filename after the safe_mode check has successfully run.
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Analysis
by VulDB Data Team • 08/12/2019
The vulnerability described in CVE-2008-2665 represents a critical directory traversal flaw within PHP's posix_access function that specifically affects versions 5.2.6 and earlier. This weakness enables remote attackers to circumvent the safe_mode security restrictions that are designed to limit file access operations in PHP applications. The vulnerability exploits a fundamental issue in how PHP handles URL canonicalization processes, creating a window where security checks can be bypassed through carefully crafted input sequences.
The technical mechanism behind this vulnerability involves the manipulation of http URLs containing dot-dot sequences that are subsequently processed through canonicalization routines. When a URL with .. sequences is processed by the posix_access function, the system first performs the safe_mode check on the original URL structure and then proceeds to canonicalize the URL to a local filesystem path. During this canonicalization process, the .. sequences are resolved in a manner that allows access to directories outside the intended safe_mode restricted areas. This temporal gap between the security check and the canonicalization process creates an exploitable condition where attackers can gain unauthorized access to files and directories that should normally be protected.
From an operational impact perspective, this vulnerability poses significant risks to web applications running vulnerable PHP versions, as it allows attackers to bypass crucial security boundaries designed to prevent unauthorized file system access. The ability to traverse directories and access restricted files can lead to complete system compromise, data theft, and further exploitation opportunities. This vulnerability particularly affects web applications that rely on safe_mode for protection, making it a serious concern for organizations maintaining legacy PHP environments. The exploitability of this vulnerability means that remote attackers can potentially access sensitive system files, configuration data, and user information without requiring local system access or elevated privileges.
The vulnerability aligns with CWE-22 Directory Traversal and follows patterns consistent with ATT&CK technique T1059 Command and Scripting Interpreter, as it enables attackers to manipulate file system access through crafted input. Organizations should immediately upgrade to PHP versions 5.2.7 or later where this vulnerability has been patched, as the fix addresses the canonicalization timing issue that allows the bypass. Additional mitigations include implementing proper input validation, restricting file access permissions, and using alternative file access methods that do not rely on the vulnerable posix_access function. Security monitoring should focus on identifying unusual file access patterns and URL manipulation attempts that might indicate exploitation attempts. The vulnerability demonstrates the importance of careful timing in security checks and the potential for canonicalization processes to introduce security gaps when not properly synchronized with access control mechanisms.