CVE-2026-109300
Received Received - Intake

Stored XSS in Open WebUI Markdown Renderer

Publication date: 2026-10-12

Last updated on: 2026-10-12

Assigner: VulnCheck

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.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published
2026-10-12
Last Modified
2026-10-12
Generated
2026-10-12
AI Q&A
2026-10-12
EPSS Evaluated
N/A
NVD
CVE-2026-109300
EUVD
EUVD-2026-97602

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
open-webui open-webui 0.6.31

Helpful Resources

Exploitability

CWE
CWE Icon
KEV
KEV Icon
CWE ID Description
CWE-79 The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

Attack-Flow Graph

AI Quick Actions

Instant insights powered by AI
Executive Summary

Open WebUI versions before 0.11.4 have a stored cross-site scripting flaw in the Markdown renderer. User-authored tool-call details are treated as tool output, and their embeds attribute is mounted in script-enabled iframes. This allows JavaScript execution in viewers' browsers when they view crafted messages or content.

Detection Guidance

Detecting this vulnerability requires checking for Open WebUI versions before 0.11.4. Inspect installed versions via package managers like npm or system package tools. Review logs for unusual JavaScript execution in user-authored tool-call details blocks or iframes.

Impact Analysis

Authenticated users can exploit this to run malicious scripts in other users' browsers. This could lead to in-app phishing attacks or session hijacking if iframeSandboxAllowSameOrigin is enabled, potentially compromising user accounts or sensitive data.

Compliance Impact

This vulnerability could potentially impact compliance with GDPR and HIPAA by enabling session hijacking or in-app phishing attacks. If exploited, it may allow unauthorized access to user sessions or sensitive data, violating confidentiality requirements under these regulations.

Mitigation Strategies

Upgrade Open WebUI to version 0.11.4 or later immediately. Disable or restrict user-authored tool-call details blocks if possible. Implement input validation for Markdown content and sanitize user inputs to prevent script execution.

Chat Assistant

Ask questions about this CVE
Hi! I’m here to help you understand CVE-2026-109300. Ask me anything about the vulnerability, its impact, or mitigation strategies.
0/70

EPSS Chart