Executive Summary

This vulnerability exists in Bitwarden Server versions before 2026.5.0 and involves privilege escalation. Authenticated Custom users who have the ManageUsers permission can exploit a missing role hierarchy check in the bulk user-remove endpoint. By sending a bulk DELETE request with Admin organization-user IDs, these users can bypass protections that normally prevent the removal of Admin accounts through the single-user removal path. As a result, one or more Admin accounts can be removed from an organization without proper authorization.

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Impact Analysis

The impact of this vulnerability is that users with limited privileges (Custom users with ManageUsers permission) can escalate their privileges by removing Admin accounts from an organization. This can lead to loss of administrative control, disruption of organizational management, and potential unauthorized changes or access within the Bitwarden Server environment.

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Mitigation Strategies

The primary mitigation is to upgrade Bitwarden Server to version 2026.5.0 or later, where this vulnerability has been fixed by adding proper role hierarchy checks in the bulk user-remove endpoint.

Until the upgrade can be applied, restrict or audit the permissions of Custom users with ManageUsers permission to prevent them from performing bulk user removals.

Additionally, monitor and log bulk DELETE requests to the user-remove endpoint to detect and respond to any suspicious activity.

Review and tighten access controls around user management functions to limit potential abuse.

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Compliance Impact

The provided information does not specify how this vulnerability directly affects compliance with common standards and regulations such as GDPR or HIPAA.

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Detection Guidance

This vulnerability involves authenticated Custom users with ManageUsers permission sending bulk DELETE requests containing Admin user IDs to the bulk user-remove endpoint to remove Admin accounts. Detection would involve monitoring for unusual or unauthorized bulk DELETE requests targeting organization Admin users.

Specifically, network or application logs should be inspected for bulk DELETE requests to the user-remove endpoint that include Admin organization-user IDs, especially if initiated by Custom users.

Suggested commands would depend on your logging and monitoring setup, but examples include:

• Using web server or application logs, grep for DELETE requests to the bulk user-remove endpoint, e.g., `grep 'DELETE /api/organization/users/bulk' /var/log/bitwarden/access.log`
• Filter logs for requests containing Admin user IDs or roles in the request body or parameters.
• Use network monitoring tools to detect unusual bulk DELETE HTTP requests from authenticated Custom users.

Since the vulnerability exploits missing role hierarchy checks, auditing user role changes and removals in the organization for unexpected Admin removals can also help detect exploitation.

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