CVE-2026-26193
Summary
Manually modifying chat history allows setting the embeds property on a response message, the content of which is loaded into an iFrame with a sandbox that has allow-scripts and allow-same-origin set, ignoring the "iframe Sandbox Allow Same Origin" configuration. This enables stored XSS on the affected chat. This also triggers when the chat is in the shared format. The result is a shareable link containing the payload that can be distributed to any other users on the instance.
Details
The flaw stems from how iFrames are constructed here:
https://github.com/open-webui/open-webui/blob/6f1486ffd0cb288d0e21f41845361924e0d742b3/src/lib/components/chat/Messages/ResponseMessage.svelte#L689-L703
messages.embeds is a user controlled property and so can be arbitrarily set by the user to a payload of their choosing. Since allowScripts and allowSameOrigin are harcoded as true here the sandboxing offers essentially no protection.
PoC
Create an arbitrary chat:
<img width="2468" height="1426" alt="image" src="https://github.com/user-attachments/assets/41e32f5c-3fa7-4208-a71f-85556eec6309" />
Edit the model response:
<img width="632" height="192" alt="image" src="https://github.com/user-attachments/assets/b1e79303-360f-46e3-8d6d-3309c3ec30af" />
<img width="2150" height="434" alt="image" src="https://github.com/user-attachments/assets/78f19d7f-10dc-4e91-83cc-2d4811e58496" />
Before saving, configure the browser to use an HTTP proxy tool (Burp/Caido/ZAP) and intercept the save request. Find the object within the history and then messages objects (not the messages array) that corresponds to the edited text.
<img width="2024" height="1528" alt="image" src="https://github.com/user-attachments/assets/953e5368-8e93-428b-b223-c695eacfe7b9" />
On this object, add an embeds key and list value as shown below, forward the request and refresh the page.
<img width="1904" height="1530" alt="image" src="https://github.com/user-attachments/assets/0e56be6f-5513-490e-9961-972bdfbd5d8b" />
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Exploitation outlook
- Low exploitation risk0.20% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 10% of all EPSS-scored CVEs.
Advisory coverage (1)
External references
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[](https://www.csirts.com/cve/CVE-2026-26193)