CVE-2021-38337 in RSVPMaker Excel Plugin
Summary
by MITRE • 09/10/2021
The RSVPMaker Excel WordPress plugin is vulnerable to Reflected Cross-Site Scripting due to a reflected $_SERVER["PHP_SELF"] value in the ~/phpexcel/PHPExcel/Shared/JAMA/docs/download.php file which allows attackers to inject arbitrary web scripts, in versions up to and including 1.1.
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Analysis
by VulDB Data Team • 09/16/2021
The vulnerability identified as CVE-2021-38337 affects the RSVPMaker Excel WordPress plugin, specifically targeting versions up to and including 1.1. This issue represents a classic reflected cross-site scripting vulnerability that exploits improper input validation within the plugin's PHPExcel component. The vulnerability manifests in the ~/phpexcel/PHPExcel/Shared/JAMA/docs/download.php file where the $_SERVER["PHP_SELF"] variable is directly reflected without adequate sanitization or encoding, creating an exploitable vector for malicious script injection.
The technical flaw stems from the plugin's failure to properly sanitize user-supplied input before incorporating it into HTTP response content. When an attacker crafts a malicious URL containing script code within the PHP_SELF parameter, this input gets reflected back to the victim's browser without proper HTML encoding or context-appropriate sanitization. This allows attackers to execute arbitrary JavaScript code within the victim's browser context, potentially leading to session hijacking, credential theft, or redirection to malicious sites. The vulnerability is categorized under CWE-79 as a failure to sanitize or incorrectly sanitize user-supplied input, making it a direct implementation of the well-known cross-site scripting attack pattern.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable sophisticated attack chains within WordPress environments. An attacker could leverage this vulnerability to establish persistent access through session manipulation or to perform actions on behalf of authenticated users. The reflected nature of the vulnerability means that the attack requires user interaction with a malicious link, typically through phishing campaigns or social engineering. This makes the vulnerability particularly dangerous in environments where users may not be security-aware, as the attack vector is often indirect and less obvious than direct server-side exploits. The vulnerability affects the entire WordPress ecosystem where the plugin is installed, potentially compromising multiple sites if the plugin is widely deployed.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security hardening. The most effective immediate solution involves updating to the latest version of the RSVPMaker Excel plugin where the XSS vulnerability has been patched. Organizations should also implement proper input validation and output encoding mechanisms to prevent similar issues in other components. The recommended defensive measures include implementing Content Security Policy headers to limit script execution, enabling proper HTTP response encoding for all dynamic content, and conducting regular security audits of third-party plugins. Additionally, implementing web application firewalls with XSS detection capabilities can provide an additional layer of protection. Security teams should also consider implementing security awareness training for users to recognize phishing attempts that may exploit this vulnerability, as the reflected nature of the attack requires user interaction to be effective. The vulnerability demonstrates the critical importance of input validation and proper output encoding practices in web application development, aligning with ATT&CK technique T1059.001 for command and scripting interpreter execution through web-based attack vectors.