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: jupyter server
References8
- github.com/jupyter-server/jupyter_server/security/advisories/GH… MitigationPatchVendor Advisory
- github.com/jupyter-server/jupyter_server/commit/057869a327c4673… Patch
- github.com/jupyter-server/jupyter_server/commit/49b34392feaa977… Patch
- github.com/jupyter-server/jupyter_server/pull/603 Issue Tracking
- access.redhat.com/errata/RHSA-2026:43038
- access.redhat.com/security/cve/CVE-2026-40110
- bugzilla.redhat.com/show_bug.cgi?id=2466912
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40110…
Metrics
- CVSS 3.1
-
7.3
HIGH
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N - CVSS 4.0
-
7.6
HIGH
Score source: CNA
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 0% percentile: 25 · as of 13 November 2026
- CWE
- CWE-777CWE-625
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.