CVE-2015-4604 in PHP
Summary
by MITRE
The mget function in softmagic.c in file 5.x, as used in the Fileinfo component in PHP before 5.4.40, 5.5.x before 5.5.24, and 5.6.x before 5.6.8, does not properly maintain a certain pointer relationship, which allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via a crafted string that is mishandled by a "Python script text executable" rule.
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Analysis
by VulDB Data Team • 05/22/2022
The vulnerability described in CVE-2015-4604 represents a critical memory management flaw within the file command's magic file processing functionality, specifically affecting PHP versions prior to the mentioned secure releases. This issue resides in the mget function implementation within softmagic.c, which is part of the Fileinfo component responsible for determining file types through content inspection rather than file extensions. The flaw manifests when processing specially crafted strings that trigger improper pointer handling during the evaluation of "Python script text executable" rules, creating a dangerous condition that can be exploited by remote attackers.
The technical root cause of this vulnerability stems from inadequate pointer relationship maintenance within the mget function, which operates as part of the file command's magic database parsing mechanism. When PHP processes file type detection using the Fileinfo extension, it relies on magic files that contain rules for identifying different file types based on their content patterns. The specific flaw occurs when the system encounters a crafted string that matches the "Python script text executable" rule, causing the mget function to manipulate memory pointers incorrectly. This improper pointer handling creates conditions where memory corruption can occur, potentially leading to application crashes or more severe consequences including arbitrary code execution.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it provides attackers with potential pathways for remote code execution on affected systems. The vulnerability affects multiple PHP version streams including 5.4.x, 5.5.x, and 5.6.x, making it particularly dangerous given the widespread adoption of these PHP versions in web applications and hosting environments. Remote attackers can exploit this flaw by uploading or providing crafted files that trigger the vulnerable code path, potentially leading to complete system compromise. The vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and demonstrates how improper pointer management can create exploitable conditions in memory handling code.
Attackers can leverage this vulnerability through various vectors including file upload functionality, content inspection services, or any application that utilizes PHP's Fileinfo extension for file type detection. The exploitation process typically involves crafting malicious input that, when processed by the mget function, triggers the corrupted pointer behavior. This vulnerability has been categorized under the ATT&CK framework as a privilege escalation or code execution technique, specifically within the context of application-level exploitation. Organizations running affected PHP versions face significant risk as the vulnerability can be exploited without authentication, making it particularly dangerous in web-facing applications. The memory corruption aspect of this vulnerability makes it suitable for advanced exploitation techniques, potentially allowing attackers to execute arbitrary code with the privileges of the affected PHP process, which typically runs as the web server user.
The recommended mitigation strategy involves immediate upgrading of affected PHP installations to versions 5.4.40, 5.5.24, or 5.6.8 respectively, which contain the necessary patches to address the pointer relationship issues in the mget function. System administrators should also implement additional security measures including input validation, file type restrictions, and monitoring for suspicious file processing activities. The vulnerability demonstrates the critical importance of proper memory management in security-sensitive code and highlights the need for thorough code reviews of core library functions that handle user input. Organizations should also consider implementing web application firewalls and additional sandboxing measures to limit the potential impact of such vulnerabilities in their environments.