CVE-2015-4025 in PHP
Summary
by MITRE
PHP before 5.4.41, 5.5.x before 5.5.25, and 5.6.x before 5.6.9 truncates a pathname upon encountering a \x00 character in certain situations, which allows remote attackers to bypass intended extension restrictions and access files or directories with unexpected names via a crafted argument to (1) set_include_path, (2) tempnam, (3) rmdir, or (4) readlink. NOTE: this vulnerability exists because of an incomplete fix for CVE-2006-7243.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 05/19/2022
This vulnerability represents a path traversal flaw in php versions prior to the specified patches, where the software incorrectly handles null byte characters within file paths. The issue stems from an incomplete remediation of CVE-2006-7243, creating a persistent security gap that attackers can exploit through specific function calls. The vulnerability manifests when php encounters a null character within a pathname, causing the system to truncate the path at that point rather than properly validating the entire path string.
The technical implementation involves four primary functions that are susceptible to this manipulation: set_include_path, tempnam, rmdir, and readlink. When attackers supply malicious input containing null bytes to these functions, the php interpreter processes only the portion of the path before the null character, effectively bypassing intended file extension restrictions. This truncation behavior allows adversaries to craft arguments that appear to target legitimate files or directories while actually accessing unexpected system resources or bypassing security controls.
The operational impact of this vulnerability extends beyond simple file access restrictions, as it enables attackers to potentially execute arbitrary code or access sensitive system information. By manipulating the path truncation behavior, an attacker could bypass directory restrictions and gain access to files that should otherwise be protected, particularly in environments where php applications handle user-supplied input through these vulnerable functions. The vulnerability is particularly dangerous in web applications where user input flows directly into these functions without proper sanitization.
This issue aligns with CWE-22 Path Traversal and CWE-170 Improper Null Termination, both of which relate to improper handling of null bytes in input validation. From an attack perspective, this vulnerability maps to techniques described in the MITRE ATT&CK framework under T1059 Command and Scripting Interpreter and T1566 Phishing, as attackers can leverage path traversal to execute malicious code or gain unauthorized access to system resources. The incomplete fix for CVE-2006-7243 demonstrates how remediation efforts can sometimes create new attack vectors if not thoroughly tested against all possible input scenarios.
Organizations should immediately upgrade to php versions 5.4.41, 5.5.25, or 5.6.9 respectively to address this vulnerability. Additionally, implementing proper input validation and sanitization measures can help mitigate the risk until full patching is achieved. Security monitoring should include detection of null byte sequences in file path handling within php applications, particularly in areas where user input is processed through the vulnerable functions mentioned in the original advisory.