Executive Summary

This vulnerability in Nextcloud Server involves a missing access check at the API level that allows an attacker to add unknown circles by their ID directly to other circles.

Circle IDs have a very high complexity (62^15), so exploitation is unlikely without prior access to a valid circle ID from another source.

If an attacker obtains a circle ID, they could use this vulnerability to track memberships by adding circles without proper authorization.

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Impact Analysis

The impact of this vulnerability is relatively low, with a CVSS score of 2.6.

An attacker with low privileges and some user interaction could potentially add unknown circles to other circles, which might allow tracking of circle memberships if they have access to circle IDs.

This could lead to unauthorized information disclosure about group memberships within the Nextcloud environment.

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Detection Guidance

This vulnerability involves a missing access check on the API level that allows adding unknown circles by their ID directly to other circles. Detection would require monitoring API calls related to circle membership modifications.

Since the vulnerability exploits the ability to add circle members by their ID, detection could involve inspecting API request logs for unusual or unauthorized circle ID additions.

No specific commands or detection tools are provided in the available resources.

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Mitigation Strategies

The primary mitigation step is to upgrade Nextcloud Server to version 32.0.7 or 33.0.1, or Nextcloud Enterprise Server to one of the patched versions (29.0.16.14, 30.0.17.8, 31.0.14.3, 32.0.7, or 33.0.1).

As a workaround, users can disable the circles app to prevent exploitation of this vulnerability.

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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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