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

Source: https://junglewise.ai/threats/cve-2026-40110-jupyter-jupyter-server-cors-bypass-via-improper-origin-validation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-05. Updated: 2026-06-30  
License: CC BY 4.0 with a link back

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](https://junglewise.ai/threats/technologies/jupyter-server), [jupyter-server (PyPI)](https://junglewise.ai/threats/technologies/pypi-jupyter-server). Vendors: [Jupyter](https://junglewise.ai/threats/vendors/jupyter), [PyPI](https://junglewise.ai/threats/vendors/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

  ```sh
  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

- [https://github.com/jupyter-server/jupyter_server/commit/057869a327c46730afede3eab0ca2d2e3e74acea](https://github.com/jupyter-server/jupyter_server/commit/057869a327c46730afede3eab0ca2d2e3e74acea)
- [https://github.com/jupyter-server/jupyter_server/commit/49b34392feaa97735b3b777e3baf8f22f2a14ed8](https://github.com/jupyter-server/jupyter_server/commit/49b34392feaa97735b3b777e3baf8f22f2a14ed8)
- [https://github.com/jupyter-server/jupyter_server/pull/603](https://github.com/jupyter-server/jupyter_server/pull/603)
- [https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-24qx-w28j-9m6p](https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-24qx-w28j-9m6p)
- [https://access.redhat.com/security/cve/CVE-2026-40110](https://access.redhat.com/security/cve/CVE-2026-40110)
- [https://bugzilla.redhat.com/show_bug.cgi?id=2466912](https://bugzilla.redhat.com/show_bug.cgi?id=2466912)
- [https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40110.json](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40110.json)

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- [Jupyter Server token leakage in 5xx error logs](https://junglewise.ai/threats/cve-2026-86049-jupyter-server-token-leakage-in-5xx-error-logs)
- [Jupyter Server stored XSS in nbconvert handlers](https://junglewise.ai/threats/cve-2026-44727-jupyter-server-stored-xss-in-nbconvert-handlers)
- [Jupyter Jupyter Server CORS bypass via improper origin validation](https://junglewise.ai/threats/cve-2026-6657-jupyter-jupyter-server-cors-bypass-via-improper-origin-validation)
- [Jupyter jupyter-server path traversal in _get_os_path](https://junglewise.ai/threats/cve-2026-5422-jupyter-jupyter-server-path-traversal-in-get-os-path)