CVE-2026-87994: Open WebUI: Channel members can overwrite another member's message via the chat completions endpoint
Open WebUI is an extensible, feature-rich, and user-friendly self-hosted AI platform. From 0.9.5 until 0.11.1, the channel branch of chatcompletion in backend/openwebui/main.py checked channel write access and channel membership for a supplied messageid but did not verify that the calling user authored the targeted message. A channel member could use the chat completions endpoint to replace another member's message while preserving the victim as the stored author, altering the conversation record without gaining access to other channels. This issue is fixed in version 0.11.1.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Open WebUIto a version that resolves this vulnerability.Fixed in 0.11.1
Event History
Frequently Asked Questions
Who can exploit this issue?
A user who is a member of a channel and has channel write access can exploit it. The issue does not allow access to messages in other channels.
What must an attacker provide to alter another member's message?
The attacker must use the chat completions endpoint with a supplied message_id for a message in a channel where they have membership and write access. The vulnerable code did not verify that the attacker authored the targeted message.
How can we tell whether our deployment is affected?
Deployments running Open WebUI from version 0.9.5 up to, but not including, 0.11.1 are affected. Version 0.11.1 contains the fix.
What is the impact on the conversation record?
An attacker can replace another channel member's message while the stored author remains the victim. This can alter the apparent channel conversation history without changing authorship metadata.