Improper Authorization in Open WebUI Chat Fork Handler

Executive Summary

This vulnerability affects Open WebUI versions 0.11.0 to 0.11.3. It involves an improper authorization flaw in the chat fork handler. Users who were previously granted write access to a shared folder but later downgraded to read-only can still exploit the POST /api/v1/chats/{id}/fork endpoint to create new chats in the original folder. The system fails to check write permissions during the fork operation, allowing unauthorized chat insertion even after access restrictions are applied.

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Detection Guidance

Check Open WebUI version with: curl -s http://localhost:8080/api/version | grep version. If version is between 0.11.0 and 0.11.3, the system is vulnerable. Review shared folder permissions and chat logs for unauthorized chat insertions in folders where users were downgraded from write to read-only access.

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Impact Analysis

The vulnerability allows attackers to insert unauthorized chats into shared folders they previously had write access to. This can lead to integrity issues, as the folder owner and members may see attacker-controlled content. It requires the attacker to have created a chat in the folder while having write access and then been downgraded to read-only.

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Mitigation Strategies

Upgrade Open WebUI to version 0.11.4 or later immediately. Review and audit shared folder permissions, revoking unnecessary write access. Monitor folder activity for suspicious chat insertions by previously downgraded users. Remove any unauthorized chats found in shared folders.

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