Jupyter Server has a CORS Origin Validation Bypass via re.match() in allow_origin_pat

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

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 · score source

EPSS

• CVE-2026-40110: 0.31% estimated exploitation activity in the next 30 days; percentile 24.28 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Jupyter Server uses re.match() to validate the Origin header against the alloworiginpat configuration. Since re.match() only anchors at the start of the string, an attacker who controls a domain like http://trusted.example.com.evil.com/ passes validation against a pattern intended to match only trusted.example.com. Impact <=2.17.0 Patches 057869a327c46730afede3eab0ca2d2e3e74acea, 49b34392feaa97735b3b777e3baf8f22f2a14ed8 Workarounds Wrap your alloworiginpat value with ^ and $ References https://github.com/jupyter-server/jupyterserver/pull/603 https://docs.python.org/3/library/re.html#re.fullmatch https://docs.python.org/3/library/re.html#re.match

Published by the source

5 May 2026, 16:54 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:50 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-24qx-w28j-9m6p

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-24qx-w28j-9m6p

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-40110

Advisory: Jupyter Server has a CORS Origin Validation Bypass via `re.match()` in `allow_origin_pat`
IDs: CVE-2026-40110, GHSA-24qx-w28j-9m6p
Record: https://patchnext.com/advisories/cve-2026-40110 (revision 3, source checked 26 Oct 2026, 13:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: jupyter-server 2.18.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI jupyter-server: affected <= 2.17.0; fixed in 2.18.0

## Suggested inspection (read-only)
- `python -m pip show jupyter-server`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on jupyter-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-24qx-w28j-9m6p (OSV record GHSA-24qx-w28j-9m6p lists affected ranges: PyPI jupyter-server >=0 <2.18.0 (fixed))
- Verified: https://github.com/advisories/GHSA-24qx-w28j-9m6p (GitHub-reviewed advisory GHSA-24qx-w28j-9m6p lists affected ranges: PyPI jupyter-server >=0 <=2.17.0)

Commands are suggestions: review each one before running it.