8.7

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-54011

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

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.6,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 vulnerability is fixed in 0.9.6.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2026-54011

CVE-2026-54011:

8.7

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

SSVC / BOD 26-04 ↗

Exploitation pocAutomatable NoTech Impact Total

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Package Name	Ecosystem	Vulnerable Versions	First Patched Version
open-webui	pip	<= 0.9.5	0.9.6

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability advisory explicitly mentioned that Open WebUI renders Mermaid blocks from Markdown files and injects the generated SVG into the DOM using innerHTML. The core of the issue is that Mermaid was configured with securityLevel: 'loose', which does not sanitize the output SVG. By comparing the git tags of the last vulnerable version (v0.9.5) and the first patched version (v0.9.6), I identified the fixing commit bf6325ff337aa131495a87a15333dc1773f2ff1f. This commit modifies the renderMermaidDiagram function in src/lib/utils/index.ts to sanitize the SVG output using DOMPurify before returning it. This confirms that renderMermaidDiagram was the vulnerable function, as it was processing potentially malicious Mermaid code and returning unsanitized SVG, which would then be rendered by a component like FilePreview.svelte, triggering the XSS.

Vulnerable functions

renderMermaidDiagram

src/lib/utils/index.ts

The function `renderMermaidDiagram` was responsible for rendering Mermaid diagrams from markdown. It directly returned the SVG output from the Mermaid library, which was configured with `securityLevel: 'loose'`. This allowed for the creation of SVG files with malicious JavaScript payloads (e.g., `javascript:alert(1)`) embedded in `href` attributes. This unsanitized SVG was then injected into the DOM via `innerHTML` in other parts of the application, leading to a stored cross-site scripting (XSS) vulnerability.

Vulnerability Intelligence
Miggo AI

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WAF Protection Rules

WAF Rule

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Reasoning

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