How severe is CVE-2026-44727?

CVE-2026-44727 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-44727 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (13th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-44727?

CVE-2026-44727 affects Jupyter Jupyter Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-44727?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-44727 have an EU (EUVD) identifier?

Yes. CVE-2026-44727 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-38347.

When was CVE-2026-44727 published?

CVE-2026-44727 was published on 2026-06-22 and last updated on 2026-06-30.

CVE-2026-44727

CVE-2026-44727 is a medium-severity vulnerability in Jupyter Jupyter Server with a CVSS 3.x base score of 5.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 5.4)
CVSS v4: 9.3
EPSS exploit prediction: 0% (13th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-38347
Weakness: CWE-79
Affected product: Jupyter Jupyter Server
Published: 2026-06-22
Last modified: 2026-06-30

Description

Jupyter Server is the backend for Jupyter web applications. Prior to 2.20, the nbconvert HTTP handlers in jupyter_server render user-authored notebook HTML under the Jupyter origin without a sandbox directive in their Content-Security-Policy. Combined with nbconvert.HTMLExporter's default non-sanitizing behavior, a notebook carrying an HTML payload in a display_data output triggers stored XSS with cookie access, full /api/* authority, and kernel RCE. This vulnerability is fixed in 2.20.

Frequently asked questions

What is CVE-2026-44727?: Jupyter Server is the backend for Jupyter web applications. Prior to 2.20, the nbconvert HTTP handlers in jupyter_server render user-authored notebook HTML under the Jupyter origin without a sandbox directive in their Content-Security-Policy. Combined with nbconvert.HTMLExporter's default non-sanitizing behavior, a notebook carrying an HTML payload in a display_data output triggers stored XSS with cookie access, full /api/* authority, and kernel RCE. This vulnerability is fixed in 2.20.
How severe is CVE-2026-44727?: CVE-2026-44727 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-44727 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (13th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-44727?: CVE-2026-44727 affects Jupyter Jupyter Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-44727?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-44727 have an EU (EUVD) identifier?: Yes. CVE-2026-44727 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-38347.
When was CVE-2026-44727 published?: CVE-2026-44727 was published on 2026-06-22 and last updated on 2026-06-30.

References

Affected products (1)

cpe:2.3:a:jupyter:jupyter_server:*:*:*:*:*:*:*:*

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