Is CVE-2026-40110 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-40110 being exploited in the wild.

How severe is CVE-2026-40110?

High severity, with a CVSS score of 7.3, published 5 May 2026.

Which products and versions are affected?

jupyter-server (PyPI) ECOSYSTEM:introduced=0,fixed=2.18.0.

Is there a fix for CVE-2026-40110?

Yes. jupyter-server (PyPI): upgrade to 2.18.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-40110 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-40110?

Check whether you run Jupyter Server or jupyter-server (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-40110: Jupyter Jupyter Server CORS bypass via improper Origin validation

CVE-2026-40110 · Severity: high · CVSS 7.3 · Published 2026-05-05

Jupyter Server, the backend for Jupyter web applications, is vulnerable to a security bypass that could allow unauthorized websites to interact with its API. Due to a flaw in how the server validates the origin of incoming requests, an attacker who controls a specifically named domain can trick the server into accepting malicious commands. This could lead to unauthorized access to user data or the ability to perform actions on behalf of a logged-in user.

Technologies: Jupyter Server, jupyter-server (PyPI). Vendors: Jupyter, PyPI.

Quick answers

Is CVE-2026-40110 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-40110 being exploited in the wild.
How severe is CVE-2026-40110?: High severity, with a CVSS score of 7.3, published 5 May 2026.
Which products and versions are affected?: jupyter-server (PyPI) ECOSYSTEM:introduced=0,fixed=2.18.0.
Is there a fix for CVE-2026-40110?: Yes. jupyter-server (PyPI): upgrade to 2.18.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-40110 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-40110?: Check whether you run Jupyter Server or jupyter-server (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

jupyter-server (PyPI): upgrade to 2.18.0 or later
```
pip install "jupyter-server>=2.18.0"
```

Technical details

Jupyter Server (<= 2.17.0) uses Python's re.match() to validate the Origin header against the allow_origin_pat configuration. Because re.match() only anchors at the beginning of a string and does not enforce a full match, a pattern like 'trusted.example.com' will incorrectly validate malicious origins such as 'trusted.example.com.evil.com'. This allows an attacker to bypass Cross-Origin Resource Sharing (CORS) protections. By enticing an authenticated user to visit a malicious site, the attacker can execute cross-origin requests to the Jupyter Server API. The vulnerability is addressed in version 2.18.0 by switching to full-string matching.

Affected products

Jupyter Jupyter Server <= 2.17.0
Red Hat Migration Toolkit for Applications 8
Red Hat Red Hat OpenShift AI (RHOAI)

Identifiers

CVE-2026-40110
GHSA-24qx-w28j-9m6p
PYSEC-2026-2187

Timeline

2026-05-05: disclosed
2026-05-05: advisory
2026-05-04: patched

References

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