CVE-2026-54011 open-webui CVE debrief

Who should care

Organizations using Open WebUI, especially those with sensitive data or high security requirements, should prioritize patching this vulnerability. The high CVSS score of 8.7 indicates a significant risk of exploitation. Security teams should ensure that all instances of Open WebUI are updated to version 0.9.6 or later.

Technical summary

The vulnerability in Open WebUI stems from insecure rendering of Mermaid blocks in Markdown previews. Mermaid is a tool for generating diagrams from text via a JavaScript-based generation. When rendering Mermaid blocks, Open WebUI uses innerHTML to insert the generated SVG into the DOM. However, Mermaid is configured with securityLevel: 'loose', which allows for the execution of JavaScript code embedded within Mermaid diagrams. An attacker can craft malicious Mermaid code that, when rendered, executes JavaScript in the context of the victim's browser. This can lead to unauthorized actions, data theft, or further exploitation. The vulnerability is particularly dangerous because it can be exploited through the Markdown preview feature, which may be accessible to users who do not typically have administrative privileges.

Defensive priority

High. Given the CVSS score of 8.7 and the potential for JavaScript execution, immediate patching is recommended.

Recommended defensive actions

• Update Open WebUI to version 0.9.6 or later.
• Review and restrict Markdown preview access to trusted users.
• Implement Content Security Policy (CSP) to mitigate potential JavaScript execution.
• Monitor for suspicious activity, especially in the Markdown preview feature.
• Consider temporarily disabling Markdown preview until the update can be applied.

Evidence notes

The CVE-2026-54011 vulnerability was validated through a working payload in the Markdown preview path. The vulnerability is fixed in Open WebUI version 0.9.6. The CVSS score of 8.7 indicates a high severity level.

Official resources