CVE-2026-32308 OneUptime: Stored XSS via Mermaid Diagram Rendering (securityLevel: "loose")
Attackers can execute arbitrary JavaScript via stored XSS in Mermaid diagrams rendered in markdown fields, potentially compromising user accounts.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-32308?
CVE-2026-32308 is a high-severity cross-site scripting vulnerability in oneuptime, published on 12 Mar 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-79
Which versions are affected by CVE-2026-32308?
2 open source packages ship an affected version, including oneuptime. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
oneuptime npm | All versions | 10.0.23 |
oneuptime npm | All versions | 10.0.23 |
Products include Hackerbay Oneuptime.
How do I fix CVE-2026-32308?
Upgrade oneuptime to 10.0.23 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-32308 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-32308 exists.
Other vulnerabilities in oneuptime
- CVE-2026-33396 Code injection in oneuptime
- CVE-2026-32306 OneUptime ClickHouse SQL Injection via Aggregate Query Parameters
- CVE-2026-30956 OneUptime has authorization bypass via client‑controlled is-multi-tenant-query header
- CVE-2026-30957 OneUptime Synthetic Monitor RCE via exposed Playwright browser object
- CVE-2026-30887 OneUptime Affected by Unsandboxed Code Execution in Probe Allows Any Project Member to Achieve RCE
Sources
Also known as GHSA-wvh5-6vjm-23qh.