CVE-2021-30487 in Server
Summary
by MITRE • 04/15/2021
In the topic moving API in Zulip Server 3.x before 3.4, organization administrators were able to move messages to streams in other organizations hosted by the same Zulip installation.
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Analysis
by VulDB Data Team • 04/21/2021
The vulnerability CVE-2021-30487 represents a critical access control flaw in the Zulip Server messaging platform that undermines the fundamental isolation mechanisms between organizations within a single installation. This issue affects versions 3.x prior to 3.4 and specifically targets the topic moving API functionality that allows administrators to reorganize message content across different streams. The flaw enables organization administrators to manipulate messages in streams belonging to other organizations, effectively bypassing the security boundaries that should separate distinct organizational domains.
The technical implementation of this vulnerability stems from insufficient authorization checks within the topic moving API endpoint. When administrators attempt to move messages between streams using the API, the system fails to validate whether the target stream belongs to the same organization as the initiating administrator. This oversight creates a privilege escalation scenario where users with organization administrator privileges can access and modify content outside their designated organizational boundaries. The flaw operates at the application logic level and does not require elevated system privileges or complex exploitation techniques, making it particularly dangerous as it can be leveraged by malicious insiders or compromised administrators.
From an operational impact perspective, this vulnerability exposes organizations to significant data integrity and confidentiality risks within multi-tenant Zulip installations. Organization administrators could potentially access sensitive communications, manipulate message content, or even disrupt the workflow of other organizations sharing the same server instance. The implications extend beyond simple data access, as administrators might alter message history, delete content, or move messages to inappropriate streams, thereby undermining the trust and operational integrity of the messaging platform. This vulnerability particularly affects organizations that rely on Zulip for secure communications where information isolation is paramount.
The vulnerability aligns with CWE-284, which addresses improper access control issues in software systems, and demonstrates how inadequate privilege validation can lead to unauthorized data access. From an ATT&CK framework perspective, this represents a privilege escalation technique that could enable adversaries to gain access to additional resources within the same system. Organizations should implement immediate mitigations including updating to Zulip Server version 3.4 or later, which includes proper authorization checks for cross-organization message movement. Additionally, administrators should review and restrict API access permissions, implement monitoring for unusual message movement activities, and conduct security audits to identify any potential abuse of this vulnerability. The fix typically involves adding proper organization boundary checks to the topic moving API to ensure that administrators can only operate within their own organization's scope, thereby maintaining the multi-tenant security model that Zulip Server relies upon for protecting organizational data isolation.