CVE-2016-0031 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-2016-0029.
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Analysis
by VulDB Data Team • 06/21/2018
The CVE-2016-0031 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 upon for daily communication. This vulnerability falls under the broader category of web application security weaknesses that can compromise user sessions and enable malicious actors to execute unauthorized code within the context of a victim's browser. The flaw enables remote attackers to inject arbitrary web script or HTML content through carefully crafted URLs, making it particularly dangerous in enterprise environments where Exchange servers serve as primary communication platforms for organizational workflows and sensitive data exchanges.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding within the OWA interface, specifically when processing user-supplied URL parameters. Attackers can craft malicious URLs that, when clicked by an authenticated user, execute JavaScript code or embed malicious HTML content within the web application's response. This occurs because the application fails to properly sanitize or escape user-provided input before rendering it in the browser context, creating a classic XSS attack vector. The vulnerability is particularly concerning as it operates within the legitimate web interface that users trust, making social engineering attacks more effective since users are less likely to suspect malicious activity within familiar application environments.
The operational impact of CVE-2016-0031 extends far beyond simple script injection, as it can enable sophisticated attack chains that compromise entire user sessions and organizational security postures. An attacker leveraging this vulnerability can steal session cookies, redirect users to phishing sites, inject malicious content into email messages, or even escalate privileges within the Exchange environment. The spoofing aspect of this vulnerability means that attackers can create convincing fake email interfaces or manipulate the display of legitimate emails to trick users into revealing credentials or performing unintended actions. This weakness directly aligns with attack patterns documented in the MITRE ATT&CK framework under the T1566 technique for Phishing and T1531 for Account Access via Social Engineering, demonstrating how this vulnerability can serve as a critical initial access point for broader compromise operations.
Organizations affected by this vulnerability should implement immediate mitigations including applying Microsoft security patches, implementing robust web application firewalls, and establishing strict input validation policies for all user-facing web applications. The CWE catalog categorizes this as a CWE-79: Improper Neutralization of Input During Web Page Generation, which emphasizes the need for proper input sanitization and output encoding mechanisms. Network segmentation strategies should be employed to limit exposure, while security monitoring solutions should be configured to detect anomalous URL patterns or suspicious script execution attempts. Additionally, user education programs should emphasize the importance of verifying URL authenticity and avoiding clicking on suspicious links, particularly those originating from email communications that may have been compromised through this vulnerability. Organizations should also consider implementing Content Security Policy headers to prevent unauthorized script execution and establish incident response procedures specifically designed to address cross-site scripting attacks targeting web-based email systems.