CVE-2007-4033 in PHP
Summary
by MITRE
Buffer overflow in the intT1_EnvGetCompletePath function in lib/t1lib/t1env.c in t1lib 5.1.1 allows context-dependent attackers to execute arbitrary code via a long FileName parameter. NOTE: this issue was originally reported to be in the imagepsloadfont function in php_gd2.dll in the gd (PHP_GD2) extension in PHP 5.2.3.
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Analysis
by VulDB Data Team • 09/28/2024
The vulnerability identified as CVE-2007-4033 represents a critical buffer overflow flaw within the t1lib library version 5.1.1, specifically within the intT1_EnvGetCompletePath function located in lib/t1lib/t1env.c. This buffer overflow occurs when processing a FileName parameter that exceeds the allocated buffer size, creating an exploitable condition that allows attackers to execute arbitrary code on the target system. The vulnerability demonstrates a classic stack-based buffer overflow pattern where insufficient input validation leads to memory corruption that can be leveraged for privilege escalation or system compromise. The flaw exists in the font handling subsystem of the t1lib library, which is commonly used for PostScript Type 1 font processing in various applications and operating systems. This vulnerability was initially reported in the context of PHP's GD2 extension, specifically within the imagepsloadfont function in php_gd2.dll, highlighting the widespread impact across different software implementations that utilize the vulnerable t1lib components. The context-dependent nature of this vulnerability means that exploitation requires specific conditions to be met, typically involving controlled input that triggers the buffer overflow during font processing operations. The issue falls under CWE-121, which describes stack-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations.
The technical implementation of this vulnerability stems from improper input validation within the intT1_EnvGetCompletePath function, which processes file names without adequate length checking or buffer size verification. When a FileName parameter exceeds the predetermined buffer limits, the function continues to write data beyond the allocated memory space, potentially overwriting critical program variables, return addresses, or other memory structures. This memory corruption can be systematically exploited by attackers who craft malicious input strings that precisely overwrite the instruction pointer or other critical execution context elements, enabling arbitrary code execution with the privileges of the affected application. The vulnerability is particularly concerning because it operates at a low level within the font processing pipeline, making it difficult to detect through standard application security measures and potentially allowing for privilege escalation when the vulnerable library is used in system-level applications. The exploitation of this vulnerability typically follows the ATT&CK technique T1059.007, which involves executing malicious code through the manipulation of program execution flow via buffer overflow conditions, and may also involve T1068, which targets local privilege escalation through the exploitation of software vulnerabilities. The attack surface is expanded by the fact that the vulnerable library is used across multiple platforms and applications, including PHP's GD2 extension, which is widely deployed in web server environments.
The operational impact of CVE-2007-4033 extends beyond simple code execution to encompass potential system compromise and data integrity violations. When exploited successfully, this vulnerability can allow attackers to gain unauthorized access to systems running vulnerable applications, potentially leading to complete system takeover or persistent backdoor installation. The vulnerability affects not only individual applications but also entire software ecosystems that rely on the t1lib library for font processing capabilities, including web servers, graphic applications, and document processing systems. Organizations running vulnerable PHP installations with GD2 extensions are particularly at risk, as the vulnerability can be exploited through web-based attacks that leverage the imagepsloadfont function to trigger the buffer overflow condition. The vulnerability's impact is compounded by the fact that it can be triggered through legitimate application usage patterns, making detection and prevention challenging. System administrators must consider that exploitation could occur through various attack vectors including web application requests, file processing operations, or even through embedded applications that utilize the vulnerable font handling libraries. The vulnerability's persistence across different software implementations means that organizations must conduct comprehensive vulnerability assessments across their entire software portfolio to identify all potentially affected systems and applications that rely on the t1lib library or PHP's GD2 extension functionality.
Mitigation strategies for CVE-2007-4033 require immediate action to address the underlying buffer overflow condition through software patching and application updates. The primary remediation involves upgrading to patched versions of t1lib that contain proper input validation and buffer size checking mechanisms, or applying vendor-specific patches that address the specific buffer overflow condition in the intT1_EnvGetCompletePath function. Organizations should also implement input validation controls at application layers to prevent overly long file name parameters from reaching the vulnerable library functions, utilizing techniques such as length limits, parameter sanitization, and input filtering. Network-based mitigations including firewall rules and web application firewalls can help prevent exploitation attempts by blocking suspicious input patterns that may trigger the buffer overflow condition. Additionally, system hardening measures should be implemented to reduce the attack surface, including disabling unnecessary font processing capabilities, restricting file system access to font libraries, and implementing proper privilege separation for applications that process user-supplied font data. The implementation of stack protection mechanisms and address space layout randomization can provide additional defense-in-depth measures that make exploitation more difficult even if the underlying vulnerability is not immediately patched. Regular security assessments and vulnerability scanning should be conducted to identify any remaining instances of the vulnerable library versions and ensure that all affected applications have been properly updated to prevent potential exploitation attempts that could lead to complete system compromise.