Stored XSS in FOSSBilling Email History Views

Executive Summary

This vulnerability is a stored cross-site scripting (XSS) issue in FOSSBilling versions 0.6.0 through 0.7.2. It occurs in the client-facing email history views where email HTML content is rendered into a JavaScript template literal without proper escaping. Specifically, the content_html field is rendered using the |raw filter, which bypasses output escaping. As a result, an attacker with admin access can inject malicious JavaScript code into email content that will execute in the browsers of clients who view their email history.

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Impact Analysis

The impact of this vulnerability is that an attacker with admin privileges can inject malicious scripts into email content. These scripts will execute in the browsers of clients viewing their email history, potentially leading to unauthorized actions such as session hijacking, data theft, or other malicious activities performed in the context of the affected user's browser.

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Detection Guidance

This vulnerability involves stored cross-site scripting (XSS) in the client-facing email history views of FOSSBilling, where malicious JavaScript payloads can be injected into email content by an attacker with admin access.

To detect this vulnerability on your system, you should audit the email content stored in the database for suspicious or malicious JavaScript payloads, especially in the HTML content fields.

Since the vulnerability is related to the rendering of email HTML content using the `|raw` filter, you can search the database for email content fields containing suspicious script tags or JavaScript event handlers.

Specific commands depend on your database system, but for example, if using MySQL, you might run queries like:

• SELECT * FROM emails WHERE content_html LIKE '%<script>%';
• SELECT * FROM emails WHERE content_html REGEXP 'onerror|onload|javascript:';

Additionally, monitor client accounts for unusual activity that might indicate exploitation.

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Mitigation Strategies

Immediate mitigation steps include:

• Restrict admin account access to trusted personnel only to reduce the risk of malicious payload injection.
• Audit the email content stored in the database for suspicious or malicious JavaScript payloads and remove or sanitize them.
• Monitor client accounts for unusual activity that could indicate exploitation of the vulnerability.
• Upgrade FOSSBilling to version 0.8.0 or later, where the vulnerability has been fixed.

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Compliance Impact

The vulnerability allows an attacker with admin access to inject malicious JavaScript into email content viewed by clients, potentially leading to unauthorized access or data exposure through cross-site scripting (XSS). This could impact compliance with standards like GDPR and HIPAA, which require protection of personal data and secure handling of client information.

Specifically, the risk of executing malicious scripts in clients' browsers may lead to data breaches or unauthorized data processing, which are violations under these regulations.

Mitigations such as restricting admin access, auditing email content, and monitoring client accounts are recommended to reduce compliance risks.

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