Summary
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.
Affected Version
main- Reproduced on
v0.8.12
Affected Code
Mermaid is initialized in permissive mode:
https://github.com/open-webui/open-webui/blob/9bd84258d09eefe7bf975878fb0e31a5dadfe0f8/src/lib/utils/index.ts#L1698
The file preview path renders Mermaid output and injects the returned SVG into the DOM:
PoC
A malicious .md file containing the follwowing contents can be used to trigger the bug:
```mermaid
flowchart LR
A[click me]
click A href "javascript:alert(document.domain)" "x"
```
Steps to reproduce:
1- Create a new chat
2- Enable Code Interpreter and browse and upload the file with .md extension.
3- Clicking on the file, and clicking click me should pop an alert
Impact
A successful exploit allows JavaScript execution in the victim’s browser under the Open WebUI origin when a malicious Markdown file is opened in the preview panel.
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
CVE-2026-54011 has a CVSS score of 8.7 (High). The vector is network-reachable, low privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.9.6); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Since mermaid has DOMPurify as a built-in, it is recommended to use the strict mode instead of loose.
Frequently Asked Questions
- What is CVE-2026-54011? CVE-2026-54011 is a high-severity cross-site scripting (XSS) vulnerability in open-webui (pip), affecting versions <= 0.9.5. It is fixed in 0.9.6. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- How severe is CVE-2026-54011? CVE-2026-54011 has a CVSS score of 8.7 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of open-webui are affected by CVE-2026-54011? open-webui (pip) versions <= 0.9.5 is affected.
- Is there a fix for CVE-2026-54011? Yes. CVE-2026-54011 is fixed in 0.9.6. Upgrade to this version or later.
- Is CVE-2026-54011 exploitable, and should I be worried? Whether CVE-2026-54011 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-54011 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-54011? Upgrade
open-webuito 0.9.6 or later.