CVE-2016-0028 in Exchange
Summary
by MITRE
Outlook Web Access (OWA) in Microsoft Exchange Server 2013 SP1, Cumulative Update 11, and Cumulative Update 12 and 2016 Gold and Cumulative Update 1 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, aka "Microsoft Exchange Information Disclosure Vulnerability."
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Analysis
by VulDB Data Team • 08/23/2022
The vulnerability identified as CVE-2016-0028 represents a significant information disclosure flaw within Microsoft Exchange Server's Outlook Web Access component. This weakness specifically affects Exchange Server 2013 versions including SP1 and Cumulative Updates 11 and 12, alongside Exchange Server 2016 versions up to Gold and Cumulative Update 1. The vulnerability stems from insufficient validation mechanisms that control how HTML content is rendered within the web-based email interface, creating a vector for malicious actors to exploit user tracking capabilities through crafted email messages.
The technical implementation of this vulnerability resides in the improper handling of IMG element loading within OWA's HTML rendering engine. When users receive specially crafted email messages containing malicious HTML code, the system fails to adequately restrict external resource loading, particularly image references that can be used to establish tracking mechanisms. This flaw operates at the application layer and leverages the inherent capabilities of HTML image tags to make HTTP requests to external servers, enabling attackers to monitor user activity and gather information about email recipients.
The operational impact of this vulnerability extends beyond simple tracking capabilities, as it enables sophisticated reconnaissance activities that can compromise user privacy and potentially facilitate more advanced attacks. Attackers can exploit this weakness to determine when users open emails, track user locations based on server response patterns, and gather metadata about user behavior within the email environment. The vulnerability is particularly concerning because it operates silently in the background, allowing attackers to collect information without user awareness or intervention, making it a valuable tool for surveillance operations.
This vulnerability aligns with CWE-200, which addresses "Information Exposure" and represents a classic example of how web application security controls can be bypassed to achieve unauthorized information gathering. The flaw also corresponds to techniques described in the MITRE ATT&CK framework under T1566, specifically "Phishing with Malicious Attachment" and T1537, "Financial Theft." The ability to track users through email interactions creates a foundation for more complex attack chains where initial reconnaissance leads to targeted phishing campaigns or credential harvesting operations.
Organizations should implement immediate mitigations including applying the relevant Microsoft security updates and patches, configuring strict HTML content filtering policies within Exchange Server, and deploying network monitoring solutions to detect unusual outbound requests from email servers. Additionally, administrative controls such as disabling external image loading in webmail interfaces, implementing email content filtering rules, and conducting regular security assessments of web-based email systems can significantly reduce the attack surface. Security teams should also consider implementing user education programs to recognize potentially malicious email content and establish incident response procedures for handling suspected tracking attempts.