CVE-2016-1904 in PHP
Summary
by MITRE
Multiple integer overflows in ext/standard/exec.c in PHP 7.x before 7.0.2 allow remote attackers to cause a denial of service or possibly have unspecified other impact via a long string to the (1) php_escape_shell_cmd or (2) php_escape_shell_arg function, leading to a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 07/03/2022
The vulnerability identified as CVE-2016-1904 represents a critical integer overflow flaw within PHP's ext/standard/exec.c file that affects PHP 7.x versions prior to 7.0.2. This vulnerability specifically targets the php_escape_shell_cmd and php_escape_shell_arg functions, which are responsible for escaping shell commands and arguments respectively. The flaw occurs when these functions process exceptionally long input strings that exceed the maximum representable value for integer data types, causing the arithmetic operations to wrap around and produce incorrect buffer size calculations. This fundamental issue stems from inadequate input validation and overflow protection mechanisms within the shell escaping functions that are commonly used in web applications to prevent command injection attacks.
The technical exploitation of this vulnerability manifests through heap-based buffer overflow conditions that can be triggered by remote attackers who supply maliciously crafted input strings to the vulnerable PHP functions. When the integer overflow occurs during the calculation of buffer sizes needed for shell command escaping, the application allocates insufficient memory or incorrectly calculates memory requirements, leading to memory corruption within the heap allocation regions. This type of vulnerability falls under CWE-190, which specifically addresses integer overflow conditions that can result in buffer overflows and memory corruption. The heap-based nature of the overflow means that the corrupted memory can affect the application's stability and potentially provide attackers with opportunities to execute arbitrary code or cause denial of service conditions.
The operational impact of CVE-2016-1904 extends beyond simple denial of service scenarios to potentially enable more sophisticated attack vectors that align with the ATT&CK framework's command and control techniques. When exploited, this vulnerability can allow attackers to cause application crashes, leading to service unavailability, or in more severe cases, potentially enable code execution through memory corruption that could be leveraged for privilege escalation or system compromise. The vulnerability is particularly concerning in web environments where PHP applications frequently process user input through shell command execution functions, making it a prime target for attackers seeking to exploit web applications that rely on shell escaping for security purposes. Organizations running affected PHP versions face significant risk exposure, especially in environments where applications may be processing untrusted input through these vulnerable functions.
Mitigation strategies for CVE-2016-1904 primarily focus on immediate patching and version updates to PHP 7.0.2 or later versions where the integer overflow protections have been implemented. System administrators should also implement input validation measures that limit the length of strings processed by shell escaping functions, thereby reducing the likelihood of triggering the overflow conditions. Additional defensive measures include implementing proper memory protection mechanisms, using sandboxed execution environments for shell commands, and applying web application firewalls that can detect and block suspicious input patterns. The vulnerability demonstrates the importance of robust integer overflow protection in security-critical code paths and highlights the necessity of comprehensive input validation in preventing memory corruption vulnerabilities that can lead to both denial of service and potential remote code execution scenarios. Organizations should conduct thorough vulnerability assessments to identify all instances where these functions are used within their PHP applications and ensure proper remediation across their entire application portfolio.