CVE-2007-1383 in PHP
Summary
by MITRE
Integer overflow in the 16 bit variable reference counter in PHP 4 allows context-dependent attackers to execute arbitrary code by overflowing this counter, which causes the same variable to be destroyed twice, a related issue to CVE-2007-1286.
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Analysis
by VulDB Data Team • 04/03/2025
The vulnerability described in CVE-2007-1383 represents a critical integer overflow condition affecting PHP 4's variable reference counting mechanism. This flaw exists within the 16-bit variable reference counter implementation that tracks how many references point to a given variable within the PHP interpreter's memory management system. The vulnerability stems from the insufficient bit width of the reference counter variable, which cannot properly handle scenarios where the reference count exceeds the maximum value that can be represented by a 16-bit signed integer, specifically 32,767. When this overflow occurs, the reference counter wraps around to a negative value or zero, creating a situation where the memory management system incorrectly believes a variable has no remaining references.
The operational impact of this vulnerability extends beyond simple memory management issues to potentially enable arbitrary code execution. Attackers can exploit this condition by carefully crafting PHP code that creates numerous references to variables, ultimately causing the reference counter to overflow and wrap around. When the counter wraps, the system may attempt to free memory associated with a variable that has already been freed, leading to a double-free condition. This memory corruption scenario creates opportunities for attackers to manipulate the execution flow of the PHP interpreter, potentially allowing them to inject and execute malicious code on the target system. The vulnerability is context-dependent, meaning it requires specific conditions to be met, such as creating a large number of variable references in a particular sequence.
This vulnerability directly relates to CWE-190, which describes integer overflow conditions, and represents a specific manifestation of improper handling of integer arithmetic within memory management systems. The issue connects to the broader category of memory safety vulnerabilities that have historically plagued interpreted languages and can be mapped to ATT&CK technique T1059.007 for command and scripting interpreter, as attackers can leverage such conditions to execute arbitrary code through PHP scripts. The double-free condition resulting from the reference counter overflow creates a classic heap corruption scenario that can be exploited to gain control over program execution flow. This type of vulnerability is particularly dangerous in web server environments where PHP scripts are executed with elevated privileges, as it can provide attackers with a pathway to compromise entire web applications and potentially underlying systems.
The mitigation strategies for this vulnerability involve upgrading to PHP 5 or later versions where the reference counting mechanism has been redesigned with larger integer types to prevent overflow conditions. Additionally, administrators should implement proper input validation and sanitization practices to prevent exploitation attempts, while also monitoring for unusual patterns of variable reference creation that might indicate attempted exploitation. The vulnerability highlights the importance of proper integer handling in memory management systems and serves as a reminder of the critical need for robust bounds checking in interpreted language implementations. Organizations should also consider implementing security patches and updates promptly, as this vulnerability was addressed in subsequent PHP releases through architectural changes to the reference counting mechanism.