CVE-2009-3546 in PHP
Summary
by MITRE
The _gdGetColors function in gd_gd.c in PHP 5.2.11 and 5.3.x before 5.3.1, and the GD Graphics Library 2.x, does not properly verify a certain colorsTotal structure member, which might allow remote attackers to conduct buffer overflow or buffer over-read attacks via a crafted GD file, a different vulnerability than CVE-2009-3293. NOTE: some of these details are obtained from third party information.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 08/24/2021
The vulnerability identified as CVE-2009-3546 represents a critical buffer overflow condition within the GD Graphics Library implementation in PHP versions 5.2.11 and 5.3.x prior to 5.3.1. This flaw exists in the _gdGetColors function located in gd_gd.c, where insufficient validation occurs for the colorsTotal structure member during GD file processing. The vulnerability stems from improper bounds checking that fails to validate the expected size of color data structures, creating opportunities for malicious actors to manipulate file parsing routines through carefully crafted GD image files. The flaw specifically affects the GD Graphics Library version 2.x and impacts PHP's image handling capabilities when processing external image data, making it particularly dangerous in web applications that accept user-uploaded images or process third-party graphics files.
The technical implementation of this vulnerability involves the _gdGetColors function's failure to properly validate the colorsTotal member of the GD file structure before attempting to read or allocate memory for color palette data. When a malformed GD file is processed, the function accepts an arbitrary value for colorsTotal without proper verification against expected bounds or maximum limits. This allows attackers to specify an excessively large number of colors that exceeds the allocated buffer space, resulting in either buffer overflow conditions that can be exploited for code execution or buffer over-read scenarios that may expose sensitive memory contents. The vulnerability operates at the intersection of image parsing logic and memory management, where the parser's trust in file metadata leads to improper memory allocation decisions.
From an operational perspective, this vulnerability presents significant risk to web applications that utilize PHP's GD library for image processing, particularly those accepting user uploads or processing external image sources. Attackers can craft malicious GD files that trigger the buffer overflow conditions when the PHP application attempts to parse these images, potentially leading to remote code execution, denial of service, or information disclosure. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, though it manifests through a different attack vector than CVE-2009-3293, which specifically addressed heap-based buffer overflows in the same library. The impact extends beyond individual application compromise to potentially affect entire web server environments where PHP-based applications process untrusted image data.
Mitigation strategies for CVE-2009-3546 primarily focus on immediate version upgrades to PHP 5.3.1 or later, where the vulnerability has been patched through enhanced bounds checking in the _gdGetColors function. Organizations should implement comprehensive input validation measures for all image file processing, including file type verification, size limitations, and content scanning before PHP processing occurs. Network-based protections such as web application firewalls can help detect and block suspicious image file patterns, while runtime protections like address space layout randomization and stack canaries may provide additional defense in depth. System administrators should also consider implementing strict file upload policies, sanitizing image data through multiple processing stages, and monitoring for unusual memory allocation patterns that might indicate exploitation attempts. The remediation process should include thorough testing of image processing functionality to ensure that the patch does not introduce regressions in legitimate image handling operations, while also establishing monitoring procedures to detect potential exploitation attempts through automated security scanning tools.