What is CVE-2026-42557?

CVE-2026-42557 is a critical-severity vulnerability in Jupyter Jupyterlab, classified under Cross-site Scripting. CVSS score: 9.6/10. Published 2026-05-13.

How severe is CVE-2026-42557?

Critical severity. CVSS v3 base score is 9.6 out of 10.

XSS in Jupyter Jupyterlab

CVE-2026-42557

jupyterlab is an extensible environment for interactive and reproducible computing, based on the Jupyter Notebook Architecture. Prior to 4.5.7, JupyterLab's HTML sanitizer allowlists data-commandlinker-command and data-commandlinker-args o…

Vulnerability class: XSS (Cross-Site Scripting)

EPSS: 0.001 (19.3th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.6 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H.

Affected products

Jupyter Jupyterlab
Jupyter Notebook — versions >= 7.0.0, < 7.5.6
Jupyterlab — versions < 4.5.7

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

security-advisories@github.com (x_refsource_CONFIRM, Mitigation, Vendor Advisory)

Frequently asked questions

What is CVE-2026-42557?: CVE-2026-42557 is a critical-severity vulnerability in Jupyter Jupyterlab, classified under Cross-site Scripting. CVSS score: 9.6/10. Published 2026-05-13.
How severe is CVE-2026-42557?: Critical severity. CVSS v3 base score is 9.6 out of 10.