CVE-2016-3378 in Exchange
Summary
by MITRE
Open redirect vulnerability in Microsoft Exchange Server 2013 SP1, 2013 Cumulative Update 12, 2013 Cumulative Update 13, 2016 Cumulative Update 1, and 2016 Cumulative Update 2 allows remote attackers to redirect users to arbitrary web sites and conduct phishing attacks via a crafted URL, aka "Microsoft Exchange Open Redirect Vulnerability."
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Analysis
by VulDB Data Team • 09/16/2022
The CVE-2016-3378 vulnerability represents a critical open redirect flaw in Microsoft Exchange Server versions including 2013 SP1 and various cumulative updates through 2016 CU2. This vulnerability stems from insufficient input validation within the Exchange Server web application's URL handling mechanisms, allowing malicious actors to craft deceptive links that appear legitimate but redirect users to attacker-controlled domains. The flaw specifically affects the authentication and redirection processes within the Exchange environment, creating a pathway for social engineering attacks that exploit user trust in official Microsoft services.
This vulnerability operates at the application layer and directly impacts the security posture of organizations relying on Exchange Server for email and collaboration services. The technical implementation flaw manifests when the web application fails to properly validate and sanitize user-supplied URL parameters before processing redirects. Attackers can construct malicious URLs that contain encoded redirect targets, bypassing normal security checks and routing users through the Exchange Server's authentication flow before redirecting them to phishing sites or malicious content. The vulnerability is classified under CWE-601 as an open redirect vulnerability, which specifically addresses the risk of unvalidated redirects and forwards that can be exploited to deceive users into visiting unintended destinations.
The operational impact of this vulnerability extends beyond simple phishing attacks, as it enables sophisticated social engineering campaigns that can compromise entire organizational security postures. When users encounter legitimate-looking Exchange authentication pages that subsequently redirect them to malicious sites, they often trust the redirection process due to the familiar interface and domain. This creates a high probability of credential theft, malware delivery, and data exfiltration attempts. The vulnerability affects both internal and external users who may access Exchange services through web browsers, making it particularly dangerous for organizations with remote workers or public email access capabilities. Security teams must consider this vulnerability in their threat modeling processes as it can serve as an initial access vector for more extensive attacks.
Organizations should implement immediate mitigations including applying the relevant Microsoft security updates and patches released for this vulnerability, while also deploying network-level controls such as URL filtering and web application firewalls to detect and block suspicious redirect attempts. The ATT&CK framework categorizes this vulnerability under T1566 as "Phishing" with potential T1071.101 as "Application Layer Protocol: Web Protocols" for the exploitation techniques used. Additional defensive measures include user education programs to recognize suspicious redirects, implementing strict email filtering policies, and monitoring for anomalous redirect patterns in web traffic logs. Organizations should also consider disabling unnecessary web access to Exchange services and implementing multi-factor authentication to reduce the impact of successful phishing attempts. The vulnerability highlights the importance of proper input validation and output encoding practices in web applications, reinforcing industry standards such as those outlined in the OWASP Top Ten and Microsoft's own security development lifecycle requirements.