CVE-2017-6485 in PHP-Calendar
Summary
by MITRE
A Cross-Site Scripting (XSS) issue was discovered in php-calendar before 2017-03-03. The vulnerability exists due to insufficient filtration of user-supplied data (errorMsg) passed to the "php-calendar-master/error.php" URL. An attacker could execute arbitrary HTML and script code in a browser in the context of the vulnerable website.
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Analysis
by VulDB Data Team • 09/04/2020
The vulnerability identified as CVE-2017-6485 represents a classic cross-site scripting flaw in the php-calendar application version prior to 2017-03-03. This type of vulnerability falls under CWE-79 which specifically addresses improper neutralization of input during web page generation, making it a critical concern for web application security. The issue manifests in the error handling mechanism of the calendar application where user-supplied data is inadequately sanitized before being rendered in the browser context. The vulnerability is particularly concerning as it occurs within the error.php file which is part of the php-calendar-master directory structure, indicating this is a legitimate file path that would be accessible to users interacting with the calendar system.
The technical exploitation of this vulnerability occurs through the errorMsg parameter that is passed to the error.php URL endpoint. When an attacker crafts malicious input containing HTML or JavaScript code and submits it through this parameter, the application fails to properly escape or filter the content before displaying it to users. This allows the malicious code to execute within the browser context of legitimate users who encounter the error page, effectively enabling the attacker to inject arbitrary scripts that can perform actions such as stealing cookies, redirecting users to malicious sites, or performing unauthorized operations on behalf of the victim. The vulnerability is classified as a reflected XSS attack since the malicious payload is reflected back to the user through the application's error handling mechanism.
From an operational perspective, this vulnerability creates significant risk for organizations using the affected php-calendar application as it allows attackers to compromise the web application's integrity and user sessions. The impact extends beyond simple script execution as it can enable more sophisticated attacks such as session hijacking, credential theft, or even privilege escalation if the calendar application is integrated with user authentication systems. According to ATT&CK framework, this vulnerability maps to T1059.007 which covers scripting languages and T1531 which addresses credential access through web application attacks. The vulnerability is particularly dangerous because it can be exploited through simple user interaction, requiring minimal technical skill to launch successful attacks against unsuspecting users.
The remediation strategy for CVE-2017-6485 involves implementing proper input validation and output encoding mechanisms throughout the application. Organizations should ensure that all user-supplied data is sanitized before being processed or displayed, particularly in error handling contexts. The solution requires implementing proper HTML escaping or encoding of all dynamic content before rendering it in the browser. This approach aligns with security best practices outlined in OWASP Top Ten and follows the principle of defense in depth. Additionally, implementing Content Security Policy (CSP) headers can provide an additional layer of protection against XSS attacks by restricting the sources from which scripts can be loaded and executed within the application context. Regular security audits and input validation testing should be conducted to prevent similar vulnerabilities from emerging in other parts of the application.