CVE-2016-3969 in Email Gateway
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in McAfee Email Gateway (MEG) 7.6.x before 7.6.404, when File Filtering is enabled with the action set to ESERVICES:REPLACE, allows remote attackers to inject arbitrary web script or HTML via an attachment in a blocked email.
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Analysis
by VulDB Data Team • 07/12/2022
The CVE-2016-3969 vulnerability represents a critical cross-site scripting flaw in McAfee Email Gateway version 7.6.x prior to 7.6.404, specifically when the File Filtering feature is configured with the ESERVICES:REPLACE action. This vulnerability resides within the email gateway's content filtering mechanisms and exploits a fundamental weakness in how the system handles file attachments that are blocked during email processing. The flaw allows remote attackers to execute malicious scripts in the context of a victim's browser by embedding malicious code within email attachments that are subsequently processed and replaced by the gateway's file filtering system.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding within the McAfee Email Gateway's file replacement functionality. When an email contains an attachment that triggers the File Filtering rule set to ESERVICES:REPLACE, the system processes the attachment and attempts to substitute it with a replacement file. However, the gateway fails to properly sanitize or encode user-supplied data from the attachment name or metadata before incorporating it into the HTML response generated for the blocked email notification. This creates an XSS vector where attacker-controlled content can be injected into the web interface, particularly affecting the email gateway's administrative console or user-facing interfaces that display information about blocked attachments.
The operational impact of this vulnerability extends beyond simple script execution, as it provides attackers with the capability to perform session hijacking, steal administrative credentials, or manipulate the email gateway's configuration. An attacker could craft malicious email attachments with specially crafted filenames containing JavaScript payloads that would execute when administrators view the blocked email notifications within the MEG interface. This could lead to complete compromise of the email gateway, potentially allowing attackers to bypass security controls, monitor email traffic, or even redirect email flows to malicious destinations. The vulnerability is particularly dangerous in enterprise environments where email gateways serve as critical security infrastructure and administrators regularly interact with email filtering reports.
Organizations affected by this vulnerability should immediately apply the vendor-provided patch version 7.6.404 or higher, which implements proper input validation and output encoding mechanisms for file replacement operations. Security teams should also implement network-based monitoring to detect suspicious email traffic patterns and consider temporary disabling of the ESERVICES:REPLACE action while applying patches. The vulnerability maps to CWE-79 - Cross-site Scripting and aligns with ATT&CK technique T1190 - Exploit Public-Facing Application, demonstrating how attackers can leverage web application vulnerabilities to gain unauthorized access to critical infrastructure. Additionally, this issue highlights the importance of proper input sanitization in security appliances and reinforces the need for comprehensive security testing of file handling mechanisms in enterprise email filtering solutions.