CVE-2026-93631: Zimbra Collaboration Suite OAuth Extension Cross-Site Request Forgery Enables Account Linking
A cross-site request forgery vulnerability in the OAuth extension of Zimbra Collaboration Suite (ZCS) Network Edition allows an attacker to link an attacker-controlled external account to a victim's mailbox. The OAuth callback does not bind its state value or authorization code to the initiating Zimbra session and instead selects the destination mailbox from the browser's current authentication cookie. On a deployment with the provider configured, an attacker can induce a signed-in victim to load a callback containing a fresh code for the attacker's provider account. This creates a persistent data source that imports attacker-controlled contacts or events. With bidirectional CalDAV synchronization, appointments subsequently created or edited in the linked calendar are also disclosed to the attacker. ZCS 10.1.16 and 10.1.20 are affected.
Affected Software
Event History
Frequently Asked Questions
Which deployments are exposed?
Zimbra Collaboration Suite Network Edition deployments running ZCS 10.1.16 or 10.1.20 are affected when the relevant external OAuth provider is configured. Exploitation also requires a victim to be signed in to Zimbra in their browser.
What does an attacker need to do to exploit this issue?
The attacker needs a fresh OAuth authorization code for an external account they control and must induce a signed-in victim to load the OAuth callback containing that code. No Zimbra account privileges are required by the attacker.
What is the likely impact after a successful account link?
The attacker-controlled external account becomes a persistent data source for the victim mailbox and can import attacker-controlled contacts or calendar events. If bidirectional CalDAV synchronization is enabled, appointments later created or edited in the linked calendar can be disclosed to the attacker.