CVE-2026-109300 Open WebUI 0.6.31 before 0.11.4 Stored XSS via Tool-Call Embeds
Authenticated users can inject JavaScript via crafted messages in Open WebUI, enabling session hijacking or phishing when specific sandbox settings are enabled.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-109300?
CVE-2026-109300 is a medium-severity cross-site scripting vulnerability in open-webui, published on 12 Oct 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
Open WebUI from 0.6.31 before 0.11.4 contains a stored cross-site scripting vulnerability in its Markdown renderer, which treats user-authored tool-call details blocks as tool output and mounts their embeds attribute in script-enabled iframes. Authenticated users can post crafted channel messages, chat messages, or citation content that runs JavaScript in viewers' browsers, enabling in-app phishing, or session hijacking where iframeSandboxAllowSameOrigin is enabled.
Weakness: CWE-79
Which versions are affected by CVE-2026-109300?
How do I fix CVE-2026-109300?
No fix has been published for CVE-2026-109300 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-109300 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-109300 exists.
Sources
Also known as GHSA-9wj4-mcm3-ppj6, GHSA-fc6p-2j86-rwxm.