CVE-2026-42266
CVE-2026-42266 — JupyterLab has an Extension Manager API/GUI Policy Discrepancy allowing 3rd party (malicious) extensions install via POST request.
JupyterLab is an extensible environment for interactive and reproducible computing, based on the Jupyter Notebook Architecture. From 4.0.0 to 4.5.6, the allow-list of extensions that can be installed from PyPI Extension Manager (allowed_extensions_uris) is not correctly enforced by JupyterLab. The PyPI Extension Manager was not contained to packages listed on the default PyPI index. This vulnerability is fixed in 4.5.7.
Published Updated Sources: cvelistV5, GitHub_M
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.
Exploitation
Unreported
no source claims exploitation
EPSS
1%
chance of exploitation in 30 days
CVSS base
8.8
HIGH
CISA SSVC assessment
Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.
Exploitation
None
none · proof-of-concept · active
Automatable
No
can an attacker script all four kill-chain steps
Technical impact
Total
partial · total control of the vulnerable component
Affected scope
The catalog records vendors and products as separate lists, not pairs, so which product belongs to which vendor is not something this page can say.
Vendors (2)
Products (3)
Every base score collected
Sources score independently and disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Source |
|---|---|---|---|---|---|
| 8.8 | CVSS 3.1 | HIGH | — | — | cvelistV5 |
Weakness & attack patterns
- CWE-88
- CWE-602
Attack patterns reported against this CVE. The ATT&CK techniques below are inferred from its weakness class.
- T1134Access Token Manipulation
- T1528Steal Application Access Token
- T1539Steal Web Session Cookie
References
8 on the record
- github.com/jupyterlab/jupyterlab/security/advisories/GHSA-37w4-hwhx-4rc4
x_refsource_CONFIRM
- github.com/jupyterlab/jupyterlab/releases/tag/v4.5.7
x_refsource_MISC
- jupyterhub.readthedocs.io/en/5.2.1/explanation/websecurity.html
x_refsource_MISC
- jupyterlab.readthedocs.io/en/latest/user/extensions.html#extension-manager-implementations
x_refsource_MISC
- access.redhat.com/security/cve/CVE-2026-42266
vdb-entry, x_refsource_REDHAT
- bugzilla.redhat.com/show_bug.cgi?id=2477072
issue-tracking, x_refsource_REDHAT
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42266.json
x_sadp-csaf-vex
- access.redhat.com/errata/RHSA-2026:43038
vendor-advisory, x_refsource_REDHAT
Elsewhere on this site
- jupyterlabevery CVE for this vendor
- redhatevery CVE for this vendor
- CWE-88other pages naming this weakness
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.