Answer in brief
CVE-2026-6658 records a Medium severity (CVSS 5.4) vulnerability in jupyter/nbconvert allows Cross-site Scripting (XSS) via unsanitized `text/vnd.mermaid` output in HTML exports. The current sources do not mark it as known exploited. The current feed maps nbconvert (pip). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 5.4. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps nbconvert (pip). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| nbconvertpip | <=7.17.0 | Not reported |
Published upstream
Jun 26, 2026
Evidence: source:ghsa:source_dates:source-dates:recordSource modified
Nov 6, 2026
Evidence: source:ghsa:source_dates:source-dates:recordFirst seen by HOL
Jun 26, 2026
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.
Quoted source text, attributed separately from HOL analysis.