CVE-2006-4484 in PHP
Summary
by MITRE
Buffer overflow in the LWZReadByte_ function in ext/gd/libgd/gd_gif_in.c in the GD extension in PHP before 5.1.5 allows remote attackers to have an unknown impact via a GIF file with input_code_size greater than MAX_LWZ_BITS, which triggers an overflow when initializing the table array.
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Analysis
by VulDB Data Team • 07/05/2019
The vulnerability identified as CVE-2006-4484 represents a critical buffer overflow flaw within the GD extension of PHP versions prior to 5.1.5. This issue specifically affects the LWZReadByte_ function located in the ext/gd/libgd/gd_gif_in.c file, which handles the parsing of gif image files. The flaw occurs when processing gif files with input_code_size parameters exceeding the MAX_LWZ_BITS constant, creating a scenario where the table array initialization triggers an overflow condition that can be exploited by remote attackers.
The technical implementation of this vulnerability stems from inadequate input validation within the GIF decompression algorithm. When a malicious gif file contains an input_code_size parameter that surpasses the predefined MAX_LWZ_BITS limit, the LWZReadByte_ function attempts to initialize a table array with insufficient bounds checking. This lack of proper boundary validation allows attackers to manipulate the memory allocation process, potentially leading to memory corruption that can be leveraged for arbitrary code execution. The vulnerability operates at the intersection of buffer management and input parsing, making it particularly dangerous as it can be triggered through image file processing without requiring special privileges or complex exploitation techniques.
From an operational standpoint, this vulnerability presents significant risk to web applications that process user-uploaded gif images or display external gif content through PHP-based systems. The remote attack vector means that simply viewing a maliciously crafted gif file or having it processed by a vulnerable PHP application can trigger the exploit. This creates widespread potential impact across web servers, content management systems, and any platform that relies on PHP's GD extension for image processing. The unknown impact aspect of this vulnerability suggests that the consequences could range from denial of service conditions to complete system compromise, depending on the specific environment and exploitation method employed by attackers.
The vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and demonstrates characteristics consistent with ATT&CK technique T1203, involving the exploitation of input validation flaws in web applications. Organizations running vulnerable PHP versions should prioritize immediate patching to address this issue, as the exploitation potential remains high due to the widespread use of PHP in web environments. Additional mitigations include implementing strict file type validation for uploaded content, disabling unnecessary image processing functions, and deploying web application firewalls that can detect and block malicious gif file patterns. The fix in PHP 5.1.5 involved proper bounds checking and input validation to prevent the overflow condition from occurring during table array initialization, establishing a robust defense against this class of vulnerability.