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CVE-2026-6658

MEDIUM Exploitation: PoC
5.4
CVSS 3.0
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.

Metadata

CVE ID
CVE-2026-6658
State
PUBLISHED
Assigner
@huntr_ai
Reserved
2026-04-20 08:17 UTC
Published
2026-06-26 09:40 UTC
Last updated
2026-06-26 10:19 UTC
Primary CWE
CWE-79
CWE-79 Improper Neutralization of Input During Web Page Gene…
Vendor / Product
jupyter / jupyter/jupyter
Sources
cve.org  ·  NVD

Severity & Metrics

5.4 MEDIUM CVSS 3.0
CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
SSVC — CISA Coordinator
Exploitation
PoC
Automatable
no
Tech. Impact
partial
Affected products (1)
VendorProductPlatformVersions
jupyter jupyter/jupyter — unspecified ≤ latest
Weakness (CWE)
CWESourceDescription
CWE-79 cna CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CVSS scores (1)
ScoreSeverityVersionSourceVector
5.4 MEDIUM 3.0 cna CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
References (1)
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