CVE-2016-0029 in Exchange Server
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in Outlook Web Access (OWA) in Microsoft Exchange Server 2016 allows remote attackers to inject arbitrary web script or HTML via a crafted URL, aka "Exchange Spoofing Vulnerability," a different vulnerability than CVE-2016-0031.
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Analysis
by VulDB Data Team • 06/21/2018
The CVE-2016-0029 vulnerability represents a critical cross-site scripting flaw discovered in Microsoft Exchange Server 2016's Outlook Web Access component, specifically affecting the web-based email interface that millions of enterprise users rely on daily. This vulnerability operates as a spoofing mechanism that enables remote attackers to execute malicious scripts within the context of a victim's browser session, creating a dangerous attack surface that extends beyond simple data theft to encompass full session hijacking capabilities. The flaw specifically manifests when users encounter crafted URLs that contain malicious payload code, which then executes in the browser context of authenticated Exchange users.
The technical exploitation of this vulnerability occurs through the manipulation of URL parameters within the Outlook Web Access interface, where the application fails to properly sanitize user-supplied input before rendering it in web responses. This inadequate input validation creates a persistent XSS vector that allows attackers to inject arbitrary HTML and JavaScript code into web pages viewed by legitimate users. The vulnerability's classification as a server-side XSS flaw means that the malicious code executes on the victim's browser rather than on the server itself, making it particularly challenging to detect and mitigate through traditional server-side security measures. The flaw essentially allows attackers to bypass normal authentication boundaries and execute code within the security context of the authenticated user's session.
The operational impact of CVE-2016-0029 extends far beyond simple script injection, as it provides attackers with the capability to establish persistent access to corporate email accounts and potentially compromise entire enterprise email infrastructures. Successful exploitation enables attackers to read, modify, and delete email messages, access calendar data, and potentially escalate privileges to gain broader system access. The vulnerability's relationship to the broader Exchange Server attack surface means that it can serve as a stepping stone for more sophisticated attacks, including credential harvesting, data exfiltration, and lateral movement within corporate networks. Organizations using Exchange Server 2016 without proper patching mechanisms face significant risk of unauthorized access to sensitive business communications and intellectual property.
Security professionals should recognize this vulnerability as a prime example of how web application flaws can create substantial attack vectors in enterprise environments, particularly when considering the ATT&CK framework's categorization of this as a web application attack pattern. The vulnerability aligns with CWE-79, which specifically addresses cross-site scripting flaws in web applications, and demonstrates the critical importance of input validation and output encoding in preventing such exploits. Mitigation strategies should include immediate deployment of Microsoft's security patches, implementation of web application firewalls, and enhanced monitoring of suspicious URL patterns within network traffic. Organizations must also consider implementing additional security controls such as content security policies, proper input sanitization procedures, and regular security assessments to prevent similar vulnerabilities from being exploited in their Exchange environments.