CVE-2006-7205 in PHP
Summary
by MITRE
The array_fill function in ext/standard/array.c in PHP 4.4.2 and 5.1.2 allows context-dependent attackers to cause a denial of service (memory consumption) via a large num value.
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Analysis
by VulDB Data Team • 07/20/2021
The vulnerability identified as CVE-2006-7205 represents a critical denial of service flaw within the PHP scripting language implementation. This weakness specifically affects the array_fill function located in the ext/standard/array.c source file of PHP versions 4.4.2 and 5.1.2. The vulnerability operates through a context-dependent attack vector where malicious actors can exploit the function's handling of the num parameter to consume excessive system memory resources. The flaw stems from inadequate input validation and memory allocation handling within the array_fill implementation, creating a scenario where improperly controlled numeric values can lead to unbounded memory consumption patterns.
The technical exploitation of this vulnerability occurs when the array_fill function receives a large numerical value for the num parameter, which directly controls the number of elements to be filled in the resulting array. In the affected PHP versions, the function fails to properly validate or limit the size of this parameter, allowing attackers to specify extremely large values that cause the system to allocate excessive memory blocks. This memory consumption behavior manifests as a gradual increase in memory usage until system resources are exhausted, effectively rendering the targeted PHP application or server unavailable to legitimate users. The vulnerability operates at the core level of PHP's array manipulation capabilities, making it particularly dangerous as it can affect any application utilizing the array_fill function regardless of the application's specific security measures.
The operational impact of CVE-2006-7205 extends beyond simple resource exhaustion to encompass broader system stability and availability concerns. When exploited successfully, this vulnerability can cause complete denial of service conditions where web applications become unresponsive or crash entirely due to memory allocation failures. The attack is particularly effective in shared hosting environments or applications with limited memory resources, where even moderate exploitation can cause system-wide disruptions. Security practitioners should note that this vulnerability aligns with CWE-770, which specifically addresses allocation of resources without limits or with inadequate limits, and demonstrates characteristics consistent with ATT&CK technique T1499.004 for network denial of service attacks. The vulnerability's persistence across multiple PHP versions indicates a fundamental flaw in the implementation that required significant code restructuring to address properly.
Mitigation strategies for this vulnerability primarily focus on immediate version upgrades to patched PHP releases where the array_fill function properly validates input parameters and implements reasonable memory allocation limits. Organizations should prioritize updating their PHP installations to versions that contain the specific fixes for this memory consumption issue, typically PHP 4.4.3 and 5.1.3 or later. Additionally, implementing input validation measures at the application level can provide defense-in-depth protection, where applications explicitly validate and sanitize any numeric parameters passed to array_fill functions. Network-level protections such as rate limiting and resource monitoring can help detect and prevent exploitation attempts, while system-level memory limits and process monitoring can provide additional safeguards against complete system exhaustion. The vulnerability serves as a reminder of the critical importance of proper resource management and input validation in server-side scripting environments, particularly when dealing with functions that manipulate array structures and memory allocation patterns.