Vulnerability · Published Jun 26, 2026 · Assigned by @huntr_ai
CVE-2026-6658Cross-site Scripting (XSS) in jupyter/nbconvert
Medium 5.4
In plain English
A medium-severity cross-site scripting in jupyter/jupyter from jupyter. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 5% of all known vulnerabilities).
Official description
A vulnerability in jupyter/nbconvert versions <= 7.17.0 allows for Cross-site Scripting (XSS) via unsanitized `text/vnd.mermaid` output in HTML exports. The `data_mermaid` block in `share/templates/lab/base.html.j2` renders `text/vnd.mermaid` cell output directly into HTML without escaping, enabling attackers to inject arbitrary HTML/JavaScript by breaking out of the `<pre>` tag. This vulnerability impacts any server using nbconvert to render notebooks as HTML, allowing attackers to execute arbitrary JavaScript in the context of users viewing the HTML export.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | nbconvert | no fix listed | DEBIAN-CVE-2026-6658 |
| Debian:13 | nbconvert | no fix listed | DEBIAN-CVE-2026-6658 |
| Debian:14 | nbconvert | no fix listed | DEBIAN-CVE-2026-6658 |
| PyPI | nbconvert | no fix listed | GHSA-9754-6rhw-gj3h |
| Ubuntu:22.04:LTS | nbconvert | no fix listed | UBUNTU-CVE-2026-6658 |
| Ubuntu:24.04:LTS | nbconvert | no fix listed | UBUNTU-CVE-2026-6658 |
| Ubuntu:25.10 | nbconvert | no fix listed | UBUNTU-CVE-2026-6658 |
| Ubuntu:26.04:LTS | nbconvert | no fix listed | UBUNTU-CVE-2026-6658 |
| Ubuntu:26.10 | nbconvert | no fix listed | UBUNTU-CVE-2026-6658 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| jupyter | jupyter/jupyter | unspecified – through latest |
Weakness: CWE-79 · Vector: CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N