CVE-2026-50054 in Collaboration Suite
Summary
by MITRE • 10/08/2026
An authorization flaw in Zimbra Collaboration Suite’s GrantRightsRequest allows an attacker with access to an authenticated account to grant another local account the loginAs right, creating persistent mailbox access and mail-sending authority that survives password changes and session expiry.
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Analysis
by VulDB Data Team • 10/08/2026
The vulnerability identified within Zimbra Collaboration Suite centers on a critical authorization flaw located in the GrantRightsRequest API endpoint. This component is designed to manage permissions for user accounts, allowing administrators or users with specific privileges to assign rights such as read, write, send-as, and login-as capabilities to other entities. The core technical deficiency lies in the insufficient validation of access control policies during the execution of this request. Specifically, an authenticated attacker who possesses a valid account within the Zimbra environment can exploit this logic error to escalate their own privileges or grant elevated permissions to another local account without requiring administrative oversight or proper authorization checks. This flaw effectively bypasses the intended security boundaries that separate standard user operations from privileged administrative actions, allowing for unauthorized modification of access control lists associated with mailboxes and system accounts.
The operational impact of this vulnerability is severe due to the nature of the rights being manipulated. By granting another account the loginAs right, an attacker can impersonate any other user within the organization, including high-privilege administrators or service accounts. This capability creates a persistent backdoor into the collaboration suite that remains active even if the compromised original account's password is changed or its session expires. The persistence of this access vector means that traditional credential rotation strategies are insufficient for remediation once exploitation has occurred. Furthermore, the ability to send mail as another user facilitates sophisticated phishing campaigns and business email compromise attacks, where messages appear to originate from legitimate internal sources, thereby increasing their likelihood of success against end-users who trust familiar sender identities.
From a classification perspective, this vulnerability aligns with CWE-269, which denotes Improper Privilege Management, specifically regarding the failure to enforce proper authorization checks for critical functions. It also maps directly to MITRE ATT&CK technique T1078, Valid Accounts, as it involves the misuse of legitimate credentials and permissions to maintain unauthorized access. The persistence mechanism described mirrors aspects of T1528, Steal Application Access Token, although in this case, the token is not stolen but rather a new permission grant is forged through API manipulation. This allows attackers to establish long-term footholds within the network infrastructure without triggering typical alerts associated with brute-force attacks or credential stuffing, as all actions are performed using valid, existing credentials and authorized-looking API calls that bypass standard security monitoring if behavioral analytics are not in place.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. Organizations running affected versions of Zimbra Collaboration Suite should immediately apply the vendor-provided patches to update the GrantRightsRequest logic with stricter authorization checks. It is crucial to verify that only users with explicit administrative roles can modify loginAs permissions, ensuring that this right cannot be granted by standard end-users or lower-privileged accounts. Additionally, implementing multi-factor authentication for all administrative accounts adds a layer of defense against credential theft that could precede such exploitation. Security teams should also audit existing user rights to identify any anomalous grants of the loginAs permission and revoke them if not explicitly required for business operations. Continuous monitoring of API usage patterns can help detect attempts to manipulate these permissions, providing an early warning system for potential privilege escalation attacks targeting collaboration platforms.