CVE-2012-1172 in PHP
Summary
by MITRE
The file-upload implementation in rfc1867.c in PHP before 5.4.0 does not properly handle invalid [ (open square bracket) characters in name values, which makes it easier for remote attackers to cause a denial of service (malformed $_FILES indexes) or conduct directory traversal attacks during multi-file uploads by leveraging a script that lacks its own filename restrictions.
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Analysis
by VulDB Data Team • 12/02/2021
The vulnerability described in CVE-2012-1172 resides within PHP's file upload handling mechanism, specifically in the rfc1867.c implementation that processes multipart/form-data requests. This flaw affects PHP versions prior to 5.4.0 and represents a critical security weakness that stems from improper validation of name values during file upload processing. The vulnerability manifests when the upload system encounters invalid opening square bracket characters within the name attributes of uploaded files, creating a scenario where malicious actors can manipulate the $_FILES superglobal array structure in unexpected ways.
The technical implementation flaw occurs at the parsing level where PHP's file upload handler fails to properly sanitize or validate the name attributes of form fields during multipart data processing. When an attacker submits a malformed upload request containing opening square brackets within name values, the parsing logic becomes confused and creates malformed $_FILES array indexes that can be exploited for various malicious purposes. This improper handling creates a path for attackers to manipulate the internal structure of file upload data, effectively bypassing normal filename validation mechanisms that would typically prevent such attacks.
The operational impact of this vulnerability extends beyond simple denial of service conditions to enable more sophisticated directory traversal attacks. Attackers can leverage this weakness during multi-file uploads to construct malicious $_FILES indexes that may result in unintended file placement on the server filesystem. The vulnerability is particularly dangerous because it allows attackers to bypass filename restrictions that are typically enforced by web applications, potentially leading to arbitrary file creation or overwriting of existing files in targeted directories. This creates opportunities for remote code execution through carefully crafted file uploads that can be executed by the web server.
The vulnerability aligns with CWE-22 Directory Traversal and CWE-434 Unrestricted Upload of File with Dangerous Type, representing a combination of path traversal and insecure file handling issues. From an ATT&CK perspective, this vulnerability maps to T1190 Exploit Public-Facing Application and T1059 Command and Scripting Interpreter, as it enables attackers to exploit web application interfaces to upload malicious files and potentially execute code. The weakness creates a persistent threat vector that can be exploited repeatedly, making it particularly concerning for web applications that handle user file uploads without proper validation and sanitization of form field names.
Organizations should immediately upgrade to PHP 5.4.0 or later versions to address this vulnerability, as the fix implemented in newer releases properly validates and sanitizes name attributes during file upload processing. Additional mitigations include implementing strict input validation for all form field names, particularly during file upload operations, and deploying web application firewalls that can detect and block malformed multipart requests. Security teams should also conduct thorough code reviews to ensure that applications do not rely solely on PHP's built-in file upload handling and implement additional validation layers to prevent similar issues in custom upload processing code.