What’s Vulnerable › Vulnerabilities

CVE-2026-40110: jupyter-server CORS origin validation bypass via unanchored regex in allow_origin_pat

• Severity: high (CVSS 7.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-05 · updated 2026-07-24
• Weakness: CWE-777

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: before 2.18.0 — fixed in 2.18.0

How to fix

Upgrade to a fixed version: jupyter-server jupyter_server 2.18.0. Check the vendor advisory for mitigations.

References

• 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/pull/603
• https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-24qx-w28j-9m6p
• https://access.redhat.com/errata/RHSA-2026:43038
• https://access.redhat.com/security/cve/CVE-2026-40110
• https://bugzilla.redhat.com/show_bug.cgi?id=2466912
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40110.json

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