CVE-2017-16962 in Communigate Pro
Summary
by MITRE
The WebMail components (Crystal, pronto, and pronto4) in CommuniGate Pro before 6.2.1 have stored XSS vulnerabilities via (1) the location or details field of a Google Calendar invitation, (2) a crafted Outlook.com calendar (aka Hotmail Calendar) invitation, (3) e-mail granting access to a directory that has JavaScript in its name, (4) JavaScript in a note name, (5) JavaScript in a task name, or (6) HTML e-mail that is mishandled in the Inbox component.
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Analysis
by VulDB Data Team • 07/06/2025
The vulnerability identified as CVE-2017-16962 represents a critical stored cross-site scripting flaw affecting CommuniGate Pro webmail components including Crystal, Pronto, and Pronto4 versions prior to 6.2.1. This vulnerability stems from inadequate input validation and sanitization mechanisms within the webmail application's handling of user-supplied data across multiple attack vectors. The flaw allows attackers to inject malicious JavaScript code that persists within the application's storage mechanisms, making it executable whenever affected pages are accessed by legitimate users. The vulnerability specifically targets the webmail interface's processing of calendar invitations from Google and Outlook.com, directory access requests, note and task naming conventions, and email content handling within the inbox component. This stored XSS vulnerability operates under CWE-79 which categorizes cross-site scripting as a weakness where applications fail to properly validate or sanitize user-provided data before incorporating it into dynamically generated web pages.
The technical exploitation of this vulnerability occurs through multiple attack surfaces that leverage the application's failure to adequately sanitize input fields. When users receive calendar invitations from Google or Outlook.com, the application processes the location or details fields without proper HTML escaping or sanitization, allowing JavaScript code to be stored and subsequently executed in the context of other users' browsers. Similarly, when directory access requests contain JavaScript within their names, or when notes and tasks are named with malicious JavaScript content, the system stores this code without proper validation. The Inbox component's mishandling of HTML emails creates another vector where attackers can embed malicious scripts that persist in the message storage and execute when messages are viewed. This vulnerability directly aligns with ATT&CK technique T1566 which covers social engineering attacks that leverage web-based exploits to compromise user systems.
The operational impact of CVE-2017-16962 extends beyond simple data theft or defacement, as it enables attackers to establish persistent footholds within the target environment. Once successfully exploited, malicious JavaScript can harvest user credentials, redirect users to phishing sites, modify email content, or even execute arbitrary commands on behalf of the compromised user. The stored nature of the vulnerability means that the malicious code remains active until the application is patched or the affected data is manually removed, potentially affecting all users who access the compromised webmail interface. Organizations using CommuniGate Pro versions prior to 6.2.1 face significant risk of credential theft, data exfiltration, and potential lateral movement within their network infrastructure through compromised user sessions. The vulnerability's persistence across multiple components suggests a systemic weakness in the application's input validation architecture that could be exploited for broader reconnaissance and attack development activities.
Mitigation strategies for CVE-2017-16962 require immediate patching of CommuniGate Pro to version 6.2.1 or later, which contains the necessary input sanitization fixes. Organizations should implement additional defensive measures including web application firewalls that can detect and block XSS patterns, enhanced email filtering systems that sanitize HTML content, and regular security assessments of webmail applications. Network administrators should consider implementing content security policies to limit script execution within the webmail environment and monitor for unusual access patterns that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of input validation in web applications and serves as a reminder of the necessity for comprehensive security testing including penetration testing and code review processes. Organizations should also consider implementing user education programs to recognize potential social engineering attempts that might leverage this vulnerability, as the attack often relies on users opening malicious calendar invitations or email messages that contain the stored XSS payloads.