CVE-2026-32308
Published: 13 March 2026
Summary
CVE-2026-32308 is a high-severity Cross-site Scripting (CWE-79) vulnerability in Hackerbay Oneuptime. Its CVSS base score is 7.6 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 17.0th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-15 (Information Output Filtering).
Deeper analysis
CVE-2026-32308 is a cross-site scripting (XSS) vulnerability (CWE-79) in OneUptime, an open-source solution for monitoring and managing online services. In versions prior to 10.0.23, the Markdown viewer component processes Mermaid diagrams using a securityLevel set to "loose," which permits interactive event bindings. The resulting SVG output is injected into the page via innerHTML, allowing attackers to leverage Mermaid's click directive to execute arbitrary JavaScript. This affects any user-input fields that render Markdown content, such as incident descriptions, status page announcements, and monitor notes. The vulnerability has a CVSS v3.1 base score of 7.6 (AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N).
An authenticated attacker with low privileges (PR:L) can exploit this vulnerability over the network (AV:N) by injecting a malicious Mermaid diagram into a vulnerable Markdown field. The attack requires low complexity (AC:L) and user interaction (UI:R), such as a victim clicking on the rendered diagram, which triggers the click directive to execute JavaScript in the context of the application (S:C). Successful exploitation enables high-impact confidentiality violations (C:H), such as stealing session cookies, tokens, or sensitive data viewed by the victim, with low integrity impact (I:L) and no availability disruption (A:N).
The OneUptime security advisory at https://github.com/OneUptime/oneuptime/security/advisories/GHSA-wvh5-6vjm-23qh details the issue and confirms the fix in version 10.0.23, which addresses the insecure Mermaid rendering configuration. Security practitioners should upgrade to 10.0.23 or later and review any custom Markdown rendering implementations for similar misconfigurations involving SVG injection or loose security policies in diagramming libraries.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-11720
Vulnerability details
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,…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
XSS vuln in public-facing Markdown/Mermaid renderer directly enables T1190 (exploit of web app), T1059.007 (arbitrary JS execution via click directive), and T1539 (session cookie/token theft as described impact).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Filters output from Markdown rendering of Mermaid diagrams to block executable JavaScript in SVG via XSS.
Validates user-supplied Markdown inputs to reject malicious Mermaid click directives before processing.
Ensures timely patching of OneUptime to version 10.0.23 or later to remediate the insecure Mermaid rendering flaw.