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

Affected: jupyter-server jupyter_server, Red Hat Migration Toolkit for Applications 8.2, Red Hat OpenShift AI (RHOAI)

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.

GHSA-24qx-w28j-9m6p — Jupyter Server has a CORS Origin Validation Bypass via `re.match()` in `allow_origin_pat`

Affected: PyPI: jupyter-server

Jupyter Server uses `re.match()` to validate the Origin header against the `allow_origin_pat` 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 `allow_origin_pat` value with `^` and `$`

### References

https://github.com/jupyter-server/jupyter_server/pull/603 https://docs.python.org/3/library/re.html#re.fullmatch https://docs.python.org/3/library/re.html#re.match

PYSEC-2026-2187

Affected: PyPI: jupyter-server