{"id":"PYSEC-2026-2759","summary":"Open WebUI: Stored XSS in Mermaid Markdown Preview","details":"## Summary\n\nOpen WebUI renders Mermaid blocks from Markdown files in the file preview panel and inserts the generated SVG into the DOM using `innerHTML`.\n\nBecause 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.\n\nThis is a confirmed stored XSS vulnerability reachable through normal product functionality.\n\n## Affected Version\n\n- `main`\n- Reproduced on `v0.8.12`\n\n## Affected Code\n\nMermaid is initialized in permissive mode:\n\nhttps://github.com/open-webui/open-webui/blob/9bd84258d09eefe7bf975878fb0e31a5dadfe0f8/src/lib/utils/index.ts#L1698\nThe file preview path renders Mermaid output and injects the returned SVG into the DOM:\n\nhttps://github.com/open-webui/open-webui/blob/9bd84258d09eefe7bf975878fb0e31a5dadfe0f8/src/lib/components/chat/FileNav/FilePreview.svelte#L133\n\n## Impact\n\nA 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.\n\n## PoC\n\nA malicious `.md` file containing the follwowing contents can be used to trigger the bug:\n````\n```mermaid\nflowchart LR\n  A[click me]\n  click A href \"javascript:alert(document.domain)\" \"x\"\n```\n````\nSteps to reproduce: \n1- Create a new chat \n2- Enable Code Interpreter and browse and upload the file with `.md` extension. \n\u003cimg width=\"331\" height=\"258\" alt=\"image\" src=\"https://github.com/user-attachments/assets/bce2b754-56d1-4da1-90a9-22bcb93269f2\" /\u003e\n3- Clicking on the file, and clicking `click me` should pop an alert\n\u003cimg width=\"1103\" height=\"485\" alt=\"image\" src=\"https://github.com/user-attachments/assets/18754486-799b-434e-a2fc-dd7c09956a29\" /\u003e\n \n\n## Remediation\n\nSince `mermaid` has `DOMPurify` as a built-in, it is recommended to use the `strict` mode instead of `loose`.","aliases":["CVE-2026-54011","GHSA-v8qj-hxv7-mgvv"],"modified":"2026-07-13T16:32:24.951226218Z","published":"2026-07-13T15:46:19.301063Z","references":[{"type":"WEB","url":"https://github.com/open-webui/open-webui/security/advisories/GHSA-v8qj-hxv7-mgvv"},{"type":"PACKAGE","url":"https://github.com/open-webui/open-webui"},{"type":"PACKAGE","url":"https://pypi.org/project/open-webui"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-v8qj-hxv7-mgvv"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-54011"}],"affected":[{"package":{"name":"open-webui","ecosystem":"PyPI","purl":"pkg:pypi/open-webui"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.9.6"}]}],"versions":["0.1.124","0.1.125","0.2.0","0.2.1","0.2.2","0.2.3","0.2.4","0.2.5","0.3.0","0.3.1","0.3.10","0.3.12","0.3.13","0.3.14","0.3.15","0.3.16","0.3.17","0.3.17.dev2","0.3.17.dev3","0.3.17.dev4","0.3.17.dev5","0.3.18","0.3.19","0.3.2","0.3.20","0.3.21","0.3.22","0.3.23","0.3.24","0.3.25","0.3.26","0.3.27","0.3.27.dev1","0.3.27.dev2","0.3.27.dev3","0.3.28","0.3.29","0.3.3","0.3.30","0.3.30.dev1","0.3.30.dev2","0.3.31","0.3.31.dev1","0.3.32","0.3.33","0.3.33.dev1","0.3.34","0.3.35","0.3.4","0.3.5","0.3.6","0.3.7","0.3.8","0.3.9","0.4.0","0.4.0.dev1","0.4.0.dev2","0.4.1","0.4.2","0.4.3","0.4.4","0.4.5","0.4.6","0.4.6.dev1","0.4.7","0.4.8","0.5.0","0.5.0.dev1","0.5.0.dev2","0.5.1","0.5.10","0.5.11","0.5.12","0.5.13","0.5.14","0.5.15","0.5.16","0.5.17","0.5.18","0.5.19","0.5.2","0.5.20","0.5.3","0.5.3.dev1","0.5.4","0.5.5","0.5.6","0.5.7","0.5.8","0.5.9","0.6.0","0.6.1","0.6.10","0.6.11","0.6.12","0.6.13","0.6.14","0.6.15","0.6.16","0.6.18","0.6.19","0.6.2","0.6.20","0.6.21","0.6.22","0.6.23","0.6.24","0.6.25","0.6.26","0.6.26.dev1","0.6.27","0.6.28","0.6.29","0.6.3","0.6.30","0.6.31","0.6.32","0.6.33","0.6.34","0.6.35","0.6.36","0.6.37","0.6.38","0.6.39","0.6.4","0.6.40","0.6.41","0.6.42","0.6.43","0.6.5","0.6.6","0.6.6.dev1","0.6.7","0.6.8","0.6.9","0.7.0","0.7.1","0.7.2","0.8.0","0.8.1","0.8.10","0.8.11","0.8.12","0.8.2","0.8.3","0.8.4","0.8.5","0.8.6","0.8.7","0.8.8","0.8.9","0.9.0","0.9.1","0.9.2","0.9.3","0.9.4","0.9.5"],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/open-webui/PYSEC-2026-2759.yaml"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N"}]}