CVE-2016-10045 in PHPMailer
Summary
by MITRE
The isMail transport in PHPMailer before 5.2.20 might allow remote attackers to pass extra parameters to the mail command and consequently execute arbitrary code by leveraging improper interaction between the escapeshellarg function and internal escaping performed in the mail function in PHP. NOTE: this vulnerability exists because of an incorrect fix for CVE-2016-10033.
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Analysis
by VulDB Data Team • 02/01/2025
The vulnerability identified as CVE-2016-10045 represents a critical remote code execution flaw in PHPMailer versions prior to 5.2.20, specifically within the isMail transport functionality. This vulnerability emerged from an improper interaction between the escapeshellarg function and internal escaping mechanisms within PHP's mail function, creating a pathway for attackers to inject malicious parameters into the mail command execution process. The flaw is particularly dangerous because it allows remote attackers to execute arbitrary code on the target system, potentially leading to complete system compromise and unauthorized access to sensitive data.
The technical root cause of this vulnerability stems from a flawed attempt to address CVE-2016-10033, which resulted in a regression that introduced new attack vectors rather than resolving the original security issue. When PHPMailer's isMail transport is utilized, it constructs shell commands to send emails through the system's mail function, but the improper handling of parameter escaping creates opportunities for command injection attacks. The escapeshellarg function, designed to escape shell arguments, fails to adequately account for the additional internal escaping that occurs within PHP's mail function, allowing attackers to manipulate the command execution flow and inject malicious parameters that bypass intended security controls.
This vulnerability operates at the intersection of multiple security domains and aligns with CWE-78, which specifically addresses OS Command Injection vulnerabilities. The attack surface is particularly concerning because it leverages legitimate system functionality to execute unauthorized commands, making detection more challenging for security monitoring systems. The operational impact extends beyond simple code execution, as successful exploitation can lead to full system compromise, data exfiltration, and persistent access through backdoor installations. Attackers can exploit this vulnerability through various means including web application input fields, API endpoints, or any interface that utilizes PHPMailer's mail transport functionality.
The remediation strategy requires immediate upgrading to PHPMailer version 5.2.20 or later, which contains the proper fix for this vulnerability. Organizations should also implement comprehensive input validation and sanitization measures to minimize potential attack surfaces, while ensuring that all web applications utilizing PHPMailer are properly configured to avoid unnecessary exposure. Security teams should conduct thorough vulnerability assessments to identify systems using affected PHPMailer versions and implement network segmentation to limit potential lateral movement if exploitation occurs. The vulnerability demonstrates the critical importance of careful patch management and thorough testing of security fixes to prevent regression vulnerabilities that can introduce new security risks rather than resolving existing ones.