CVE-2017-6099 in PayPal PHP Merchant SDK
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in GetAuthDetails.html.php in PayPal PHP Merchant SDK (aka merchant-sdk-php) 3.9.1 allows remote attackers to inject arbitrary web script or HTML via the token parameter.
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Analysis
by VulDB Data Team • 08/25/2024
The CVE-2017-6099 vulnerability represents a critical cross-site scripting flaw discovered in the PayPal PHP Merchant SDK version 3.9.1, specifically within the GetAuthDetails.html.php component. This vulnerability exposes web applications integrating the SDK to significant security risks by allowing malicious actors to inject arbitrary web scripts or HTML content through the token parameter. The flaw exists at the input validation and output encoding level, where user-supplied data is not properly sanitized before being rendered in the web interface. The vulnerability is particularly concerning as it affects the authentication and authorization flow of PayPal transactions, potentially enabling attackers to manipulate the payment processing environment.
This XSS vulnerability operates through the token parameter which is typically used to maintain session state and authentication context during PayPal payment transactions. When the SDK processes this parameter without adequate sanitization, it creates an injection point where malicious scripts can be executed in the context of authenticated users' browsers. The vulnerability falls under CWE-79 which specifically addresses cross-site scripting flaws in web applications, where improper validation or sanitization of user-provided data leads to unauthorized script execution. The attack vector is particularly dangerous because it can be exploited by attackers who gain access to valid token values through various means including session hijacking, man-in-the-middle attacks, or by intercepting legitimate transactions.
The operational impact of this vulnerability extends beyond simple script injection to potentially enable more sophisticated attacks such as session hijacking, credential theft, and financial fraud. When an authenticated user visits a page containing malicious content injected through the vulnerable token parameter, the attacker can execute scripts that steal session cookies, redirect users to phishing sites, or manipulate transaction data. This vulnerability directly impacts the integrity and confidentiality of payment processing workflows, potentially allowing attackers to modify payment details, redirect funds, or gain unauthorized access to merchant accounts. The attack surface is broad as any application using the affected PayPal SDK version could be compromised, particularly those that do not implement additional security measures such as Content Security Policy headers or proper input validation.
Organizations should immediately implement multiple layers of mitigation strategies to address this vulnerability. The primary remediation involves updating to a patched version of the PayPal PHP Merchant SDK where the token parameter is properly sanitized and validated. Additionally, implementing proper output encoding for all user-supplied parameters, particularly those used in HTML contexts, will prevent script execution even if the vulnerability is not fully patched. Security measures such as Content Security Policy headers should be enforced to limit script execution permissions, while input validation should be strengthened to reject malformed or suspicious data patterns. The vulnerability also highlights the importance of following secure coding practices and adhering to OWASP Top Ten security guidelines, particularly those addressing input validation and output encoding. Organizations should conduct comprehensive security testing including dynamic application security testing and manual penetration testing to identify similar vulnerabilities in their payment processing systems and ensure compliance with PCI DSS standards that govern payment card data security.