CVE-2015-7776 in Garoon
Summary
by MITRE
Cybozu Garoon 3.x and 4.x before 4.2.0 does not properly restrict loading of IMG elements, which makes it easier for remote attackers to track users via a crafted HTML e-mail message, a different vulnerability than CVE-2016-1196.
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Analysis
by VulDB Data Team • 01/31/2019
The vulnerability identified as CVE-2015-7776 affects Cybozu Garoon versions 3.x and 4.x prior to 4.2.0, representing a significant security flaw in email client handling capabilities. This issue specifically pertains to the improper restriction of IMG element loading within the email rendering system, creating a vector for user tracking through malicious email content. The vulnerability operates at the application layer and is classified under CWE-200, which deals with information exposure, making it particularly concerning for privacy-sensitive environments where email tracking could compromise user confidentiality.
The technical implementation of this vulnerability allows remote attackers to embed malicious image elements within HTML email messages that can be used to track user activities across different systems. When users open these crafted emails, the IMG elements attempt to load external resources that can be configured to log access attempts, thereby enabling attackers to monitor user behavior and potentially identify when individuals access specific emails. This tracking capability operates through the HTTP protocol and leverages the automatic image loading features of email clients, making it particularly stealthy and difficult to detect without proper network monitoring.
The operational impact of CVE-2015-7776 extends beyond simple privacy concerns to encompass potential security breaches and targeted attacks. Attackers can utilize this vulnerability to build detailed profiles of email recipients, tracking their online activities and potentially correlating this data with other intelligence sources. The vulnerability is particularly dangerous in corporate environments where sensitive information flows through email systems, as it could enable adversaries to map communication patterns and identify key personnel or critical business processes. This tracking capability aligns with ATT&CK technique T1566, which covers spearphishing campaigns that leverage email-based tracking mechanisms.
The vulnerability's classification as a user tracking mechanism places it within the broader context of privacy-preserving email security measures and highlights the importance of proper content filtering and image loading restrictions. Organizations using Cybozu Garoon systems are particularly vulnerable to this type of attack because the flaw exists in the core rendering engine rather than being a configuration issue that could be easily remediated through policy changes. The attack vector requires minimal technical expertise to implement, making it accessible to threat actors of varying skill levels and increasing the overall risk exposure for affected organizations.
Mitigation strategies for CVE-2015-7776 primarily focus on updating to Cybozu Garoon 4.2.0 or later versions, which contain proper restrictions on IMG element loading and enhanced email security features. Organizations should also implement network-level filtering to prevent external image loading from untrusted sources, configure email client security settings to disable automatic image loading, and establish monitoring procedures to detect suspicious email patterns. The remediation process should include comprehensive testing of email systems to ensure that the update does not disrupt legitimate business communications while effectively addressing the tracking vulnerability. Additionally, security awareness training for end users regarding the risks of opening suspicious emails can provide an additional layer of defense against exploitation attempts.