# CVE-2026-40110

## Summary

- **CVE ID:** CVE-2026-40110
- **Severity:** HIGH
- **CVSS Score:** 7.6 (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:L/SC:L/SI:L/SA:L)
- **CWE:** CWE-777
- **Published:** May 5, 2026
- **Last Modified:** Jul 22, 2026

## Description

Jupyter Server is the backend for Jupyter web applications. In versions 2.17.0 and earlier, the Origin header validation uses Python's re.match() to check incoming origins against the allow_origin_pat configuration value. Because re.match() only anchors at the start of the string and does not require a full match, a pattern intended to match only a trusted domain (e.g., trusted.example.com) will also match any origin that begins with that domain followed by additional characters (e.g., trusted.example.com.evil.com). An attacker who controls such a domain can bypass the CORS origin restriction and make cross-origin requests to the Jupyter Server API from an untrusted site. This issue has been fixed in version 2.18.0.

## Affected Products

- jupyter-server — jupyter_server (<= 2.17.0)

## References

- [CNA](https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-24qx-w28j-9m6p)
- [CNA](https://github.com/jupyter-server/jupyter_server/pull/603)
- [CNA](https://github.com/jupyter-server/jupyter_server/commit/057869a327c46730afede3eab0ca2d2e3e74acea)
- [CNA](https://github.com/jupyter-server/jupyter_server/commit/49b34392feaa97735b3b777e3baf8f22f2a14ed8)
- [redhat-SADP](https://access.redhat.com/security/cve/CVE-2026-40110)
- [redhat-SADP](https://bugzilla.redhat.com/show_bug.cgi?id=2466912)
- [redhat-SADP](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40110.json)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:43038)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.34%
- **EPSS Percentile:** 27.1

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._