CVE-2016-0138 in Exchange
Summary
by MITRE
Microsoft Exchange Server 2007 SP3, 2010 SP3, 2013 SP1, 2013 Cumulative Update 12, 2013 Cumulative Update 13, 2016 Cumulative Update 1, and 2016 Cumulative Update 2 misparses e-mail messages, which allows remote authenticated users to obtain sensitive Outlook application information by leveraging the Send As right, aka "Microsoft Exchange Information Disclosure Vulnerability."
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Analysis
by VulDB Data Team • 09/16/2022
The vulnerability identified as CVE-2016-0138 represents a significant information disclosure flaw within Microsoft Exchange Server versions spanning 2007 through 2016, specifically affecting organizations utilizing various service packs and cumulative updates. This vulnerability stems from the improper parsing of email messages within the Exchange infrastructure, creating a pathway for malicious actors to extract sensitive Outlook application data. The flaw particularly impacts environments where users possess the Send As right, which grants them the ability to send email messages on behalf of other users, thereby creating an attack surface that extends beyond typical user privileges.
The technical implementation of this vulnerability involves a misparsing mechanism that occurs during the processing of email messages within the Exchange Server's message handling pipeline. When legitimate users with the Send As right attempt to send messages, the system fails to properly validate or sanitize the email content, allowing attackers to craft specially formatted messages that trigger the information disclosure behavior. This misparsing creates a condition where sensitive metadata and application-specific information can be inadvertently exposed to authenticated users who should not have access to such data. The vulnerability operates at the application layer and leverages existing authentication mechanisms rather than requiring additional exploitation techniques, making it particularly dangerous in environments where legitimate administrative rights exist.
The operational impact of CVE-2016-0138 extends beyond simple information disclosure, as the sensitive Outlook application information that can be obtained may include user identifiers, email headers, message routing information, and potentially authentication tokens or session data. This exposure creates risks for organizations where Exchange Server serves as the primary email infrastructure, as attackers could potentially use the gathered information to conduct further attacks such as credential harvesting, social engineering campaigns, or targeted phishing operations. The vulnerability's remote nature means that attackers can exploit it from outside the network perimeter, provided they have legitimate authentication credentials and the Send As rights within the target environment.
Organizations affected by this vulnerability should prioritize immediate remediation through the application of Microsoft security patches and updates specifically designed to address the message parsing flaw. The mitigation strategy should include comprehensive review and restriction of Send As permissions across the Exchange environment, limiting the scope of users who possess this elevated privilege. Security teams should also implement network monitoring to detect unusual email message processing patterns that might indicate exploitation attempts. This vulnerability aligns with CWE-200, which addresses improper information disclosure, and represents a significant concern within the ATT&CK framework under the information gathering and credential access phases, where adversaries seek to extract useful information from compromised systems. The attack surface is particularly concerning in enterprise environments where Exchange Server is widely deployed and where legitimate administrative rights may be more broadly distributed than anticipated.
The broader implications of this vulnerability highlight the critical importance of proper input validation and sanitization within email processing systems, as well as the necessity of maintaining strict privilege controls within collaborative environments. Organizations should conduct thorough security assessments of their email infrastructure to identify any other potential parsing vulnerabilities and implement robust monitoring controls to detect anomalous behavior in email message handling operations. The vulnerability also underscores the importance of timely patch management and the need for organizations to maintain current security updates across all their Microsoft Exchange Server installations to prevent similar information disclosure scenarios.