CVE-2016-6845 in OX AppSuite
Summary
by MITRE
An issue was discovered in Open-Xchange OX App Suite before 7.8.2-rev8. Script code within hyperlinks at HTML E-Mails is not getting correctly sanitized when using base64 encoded "data" resources. This allows an attacker to provide hyperlinks that may execute script code instead of directing to a proper location. Malicious script code can be executed within a user's context. This can lead to session hijacking or triggering unwanted actions via the web interface (sending mail, deleting data etc.).
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Analysis
by VulDB Data Team • 10/08/2022
The vulnerability CVE-2016-6845 represents a critical cross-site scripting flaw in Open-Xchange OX App Suite versions prior to 7.8.2-rev8, specifically affecting the email client's handling of base64 encoded data resources within HTML email messages. This issue stems from insufficient input validation and sanitization mechanisms that fail to properly process script code embedded within hyperlinks of HTML emails. The vulnerability manifests when the application processes base64 encoded "data" URLs in email content, allowing malicious actors to craft HTML emails containing embedded scripts that execute within the user's browser context. This flaw directly maps to CWE-79 Improper Neutralization of Input During Web Page Generation, which classifies improper sanitization of user-controllable data as a primary weakness leading to XSS attacks.
The technical exploitation of this vulnerability occurs through the improper handling of base64 encoded data URIs in HTML email hyperlinks, where the application fails to adequately sanitize or validate the content before rendering it in the user interface. When a user opens an email containing maliciously crafted HTML with base64 encoded script content, the application processes the data URI without proper security checks, effectively executing the embedded script code within the user's browser session. This creates a persistent threat vector that can be leveraged for session hijacking attacks, where an attacker gains unauthorized access to user sessions and can perform actions on behalf of the victim. The attack surface extends beyond simple script execution to include unauthorized actions such as sending emails, deleting data, or modifying user settings through the web interface, all executed within the victim's authenticated context.
The operational impact of this vulnerability extends beyond individual user compromise to potentially affect entire organizational email infrastructures. Attackers can craft sophisticated phishing campaigns that appear legitimate while silently executing malicious payloads, making detection difficult and increasing the likelihood of successful exploitation. The vulnerability's persistence across multiple user sessions and its ability to operate within the trusted context of the email application creates a significant risk for data exfiltration, privilege escalation, and unauthorized system access. Organizations using affected versions of OX App Suite face potential data breaches, unauthorized access to sensitive information, and possible compliance violations due to the exposure of user session tokens and personal data. This vulnerability directly aligns with ATT&CK technique T1566.001 Phishing, where attackers leverage email-based attacks to deliver malicious content that exploits client-side vulnerabilities.
Mitigation strategies for CVE-2016-6845 require immediate application of the vendor-provided security patch to version 7.8.2-rev8 or later, which implements proper input sanitization for base64 encoded data resources. Organizations should also implement additional defensive measures including email content filtering, web application firewalls, and enhanced email security solutions that can detect and block suspicious base64 encoded content in email messages. Network administrators should consider implementing email security policies that restrict or sanitize base64 encoded content in incoming emails, particularly from external sources. Regular security assessments and penetration testing should be conducted to identify similar vulnerabilities in other email applications and web-based systems. Additionally, user education programs should emphasize the importance of not clicking on suspicious links in emails, even when they appear to come from trusted sources, as the vulnerability can be exploited through seemingly legitimate communication channels.