CVE-2026-115474 in Zulip
Summary
by MITRE • 11/04/2026
Zulip is an open-source team collaboration tool. From 8.0 until 12.2, in organizations where the Who can view all other users in the organization setting restricted guests from viewing other users, saving or editing a direct message draft did not verify that the sender could access the draft recipients. A guest could thereby gain access to otherwise restricted users' profile information without sending a message. Organizations that did not restrict guest access were unaffected. This issue is fixed in version 12.2.
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified within Zulip versions ranging from 8.0 through 12.2 represents a critical authorization flaw rooted in the application's handling of direct message drafts for guest users. In environments where organizational policies explicitly restrict guests from viewing other user profiles, this security control was bypassed during the specific workflow of saving or editing a draft message. The core technical failure lies in the absence of an access control check when persisting draft data to the backend storage systems. While the application correctly enforces visibility restrictions when users actively browse the directory or view profile pages, it fails to validate whether the authenticated guest user possesses the requisite permissions for each recipient listed in a draft before allowing that draft to be saved. This discrepancy between active viewing and passive data persistence creates an exploitable gap where sensitive information can be extracted without triggering standard UI-based access denials.
From a technical perspective, this issue is classified as an Insecure Direct Object Reference or more accurately, a Broken Access Control vulnerability involving indirect object references within the draft management subsystem. The attacker leverages the ability to create and save drafts containing recipient identifiers that they are not authorized to view. By inspecting the saved draft data through available API endpoints or client-side storage mechanisms, the guest user can retrieve profile information associated with those restricted recipients. This effectively circumvents the intended isolation between guests and full members of the organization. The flaw is particularly insidious because it does not require complex exploitation techniques; rather, it relies on standard application functionality that was improperly secured against unauthorized data access.
The operational impact of this vulnerability allows guest users to enumerate user profiles and gather personal or professional information about other team members who should remain invisible according to organizational policy. This exposure can lead to privacy violations and potentially aid in further social engineering attacks if the gathered profile details are used for pretexting. For organizations that rely on strict separation between external collaborators and internal staff, this flaw undermines trust and compliance with data governance standards. It is important to note that only organizations utilizing settings that restrict guest visibility were affected; those allowing guests full access to user directories remained unaffected by this specific bypass mechanism.
To mitigate the risks associated with this vulnerability, administrators must ensure that all Zulip instances are upgraded to version 12.2 or later, where the patch for this authorization check has been implemented. The fix involves adding rigorous validation logic during the draft save and edit operations to verify user permissions against each recipient before allowing data persistence. Until an upgrade is performed, organizations should monitor logs for unusual patterns in direct message interactions involving guest accounts, although detection may be challenging given that the action appears as a standard drafting activity. Adhering to the principle of least privilege during application configuration remains essential, and regular security audits of access control lists are recommended to identify similar discrepancies in other modules of the collaboration platform. This incident aligns with CWE-269 regarding Improper Privilege Management and reflects common pitfalls found in ATT&CK techniques related to unauthorized data access via API or client-side manipulation.