Bug 2466912 (CVE-2026-40110)

Summary:	CVE-2026-40110 jupyter-server: Jupyter Server: Cross-Origin Resource Sharing (CORS) bypass via improper Origin header validation
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	bbrownin, dfreiber, drow, jburrell, jkoehler, ljawale, lphiri, luizcosta, nweather, rbobbitt, rhel-process-autobot, rjohnson, sdawley, teagle, vkumar, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
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Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in Jupyter Server. The Origin header validation, which uses Python's `re.match()` function, does not correctly validate incoming origins against allowed patterns. This allows a remote attacker to bypass Cross-Origin Resource Sharing (CORS) restrictions by crafting a malicious domain that partially matches a trusted one. Consequently, the attacker can make unauthorized cross-origin requests to the Jupyter Server API from an untrusted site, potentially leading to sensitive information disclosure or other unauthorized actions.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
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Description OSIDB Bzimport 2026-05-05 22:01:32 UTC

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.