CVE-2026-54011: Open WebUI: Stored XSS in Mermaid Markdown Preview

June 17, 2026 (updated July 20, 2026)

Open WebUI renders Mermaid blocks from Markdown files in the file preview panel and inserts the generated SVG into the DOM using innerHTML.

Because Mermaid is configured with securityLevel: 'loose', attacker-controlled Mermaid content can be rendered unsafely in this flow. A working payload was validated through the Markdown preview path, resulting in JavaScript execution in the victim’s browser under the application origin.

This is a confirmed stored XSS vulnerability reachable through normal product functionality.

References

github.com/advisories/GHSA-v8qj-hxv7-mgvv
github.com/open-webui/open-webui
github.com/open-webui/open-webui/security/advisories/GHSA-v8qj-hxv7-mgvv
github.com/pypa/advisory-database/tree/main/vulns/open-webui/PYSEC-2026-2759.yaml
nvd.nist.gov/vuln/detail/CVE-2026-54011
pypi.org/project/open-webui

Code Behaviors & Features

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