CVE-2006-4486 in PHP
Summary
by MITRE
Integer overflow in memory allocation routines in PHP before 5.1.6, when running on a 64-bit system, allows context-dependent attackers to bypass the memory_limit restriction.
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Analysis
by VulDB Data Team • 07/05/2019
The vulnerability described in CVE-2006-4486 represents a critical integer overflow flaw that affected PHP versions prior to 5.1.6, specifically when operating on 64-bit systems. This issue stems from improper handling of memory allocation calculations within PHP's internal routines, creating a scenario where attackers could manipulate memory limit restrictions through carefully crafted input sequences. The vulnerability is classified under CWE-190 as an integer overflow condition, which occurs when a program attempts to perform arithmetic operations on integer values that exceed the maximum representable value for the data type. The flaw manifests particularly on 64-bit architectures where the memory allocation functions fail to properly validate the size parameters during memory requests.
The technical exploitation of this vulnerability relies on the specific behavior of integer arithmetic on 64-bit systems where certain memory allocation calculations can produce unexpected results due to overflow conditions. When PHP processes memory allocation requests, it calculates the required memory size and compares this against the configured memory_limit directive. However, in the affected versions, the integer overflow causes the calculated memory requirement to wrap around to a much smaller value, effectively allowing attackers to allocate memory that exceeds the configured limit. This occurs because the system fails to properly check for integer overflow conditions during the calculation process, particularly when dealing with large memory allocation requests that exceed the maximum value that can be represented by the integer data type.
The operational impact of this vulnerability extends beyond simple memory consumption issues, as it fundamentally undermines PHP's security model for memory management. Attackers can leverage this weakness to bypass critical security controls that are designed to prevent resource exhaustion attacks and limit the memory consumption of individual PHP processes. This creates opportunities for various malicious activities including denial of service attacks where systems can be made unresponsive through excessive memory allocation, or potentially more sophisticated attacks that exploit the memory layout to achieve privilege escalation or code execution. The vulnerability affects web applications running on 64-bit PHP installations, making it particularly relevant for enterprise environments where such systems are commonly deployed.
Mitigation strategies for this vulnerability primarily focus on immediate software updates and system hardening measures. The most effective solution involves upgrading to PHP version 5.1.6 or later, where the integer overflow conditions have been properly addressed through enhanced input validation and memory allocation routines. Organizations should also implement additional monitoring and logging of memory allocation patterns to detect potential exploitation attempts. Security configurations should include regular patch management processes and vulnerability scanning to identify systems running vulnerable PHP versions. The remediation process aligns with ATT&CK technique T1496 which involves resource hijacking through memory exhaustion, and addresses the broader category of privilege escalation vulnerabilities that can arise from improper input validation. System administrators should also consider implementing additional security controls such as process isolation, memory limit enforcement, and runtime application protection to further reduce the attack surface and prevent exploitation of similar vulnerabilities.