CVE-2016-3406 in Zimbra Collaboration
Summary
by MITRE
Multiple cross-site request forgery (CSRF) vulnerabilities in Zimbra Collaboration before 8.7.0 allow remote attackers to hijack the authentication of unspecified victims via vectors involving (1) the Client uploader extension or (2) extension REST handlers, aka bugs 104294 and 104456.
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2016-3406 represents a critical cross-site request forgery issue affecting Zimbra Collaboration software versions prior to 8.7.0. This flaw resides in the web-based administrative interface and client extensions of the email server platform, creating a significant security risk that could be exploited by remote attackers to compromise user accounts and system integrity. The vulnerability manifests through two distinct attack vectors involving the Client uploader extension and extension REST handlers, demonstrating the widespread nature of the CSRF flaw within the Zimbra ecosystem. These issues were catalogued as bugs 104294 and 104456 respectively, highlighting the complexity and scope of the authentication bypass mechanisms present in the affected software versions.
The technical implementation of this CSRF vulnerability stems from insufficient validation of request origins and lack of proper anti-CSRF token implementation within the affected components. When users navigate to malicious websites or receive crafted email attachments that trigger requests to the Zimbra server, the authentication cookies are automatically included in these requests due to the browser's automatic cookie handling behavior. This allows attackers to perform authenticated actions on behalf of victims without their knowledge or consent. The flaw specifically impacts the Client uploader extension which handles file uploads and the REST handlers that manage extension functionalities, both of which fail to properly validate the source of incoming requests or implement adequate protection mechanisms against cross-site request forgery attacks.
The operational impact of CVE-2016-3406 extends beyond simple account hijacking to potentially enable full system compromise through privilege escalation and data manipulation. Attackers could leverage these vulnerabilities to upload malicious files through the uploader extension, execute arbitrary code on the server, or modify user configurations and permissions. The attack surface is particularly concerning because Zimbra serves as an enterprise email platform where users often have elevated privileges and access to sensitive corporate data. Additionally, the REST handlers that lack proper CSRF protection could be exploited to manipulate extension configurations, potentially leading to persistent backdoors or further exploitation of other system components. This vulnerability directly violates the principle of least privilege and undermines the security model of the platform by allowing unauthorized modifications to authenticated sessions.
Organizations running affected Zimbra Collaboration versions should prioritize immediate remediation through the official 8.7.0 release which addresses these CSRF vulnerabilities through proper token validation mechanisms and enhanced request origin checking. The implementation of anti-CSRF tokens within the affected components aligns with recommended practices outlined in CWE-352, which specifically addresses cross-site request forgery vulnerabilities. Security teams should also implement network-level protections such as web application firewalls that can detect and block suspicious request patterns, while monitoring for unusual upload activities or REST API access that might indicate exploitation attempts. The mitigation strategy should include comprehensive user education regarding the dangers of clicking suspicious links or opening untrusted attachments, as social engineering remains a critical component in successful CSRF attacks. Additionally, implementing strict access controls and monitoring for unauthorized administrative activities will help detect potential exploitation of these vulnerabilities in environments where immediate patching may not be immediately possible. The ATT&CK framework categorizes this vulnerability under privilege escalation and credential access techniques, emphasizing the need for layered security approaches that protect against both automated exploitation and manual attack vectors.