Jupyter Server has a CORS Origin Validation Bypass via `re.match()` in `allow_origin_pat`
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
describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2026-40110US | high7.3 | — | ||
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… | ||||
references
External citations — patches, advisories, analysis.
- https://access.redhat.com/errata/RHSA-2026:43038WEB
- https://access.redhat.com/security/cve/CVE-2026-40110WEB
- https://bugzilla.redhat.com/show_bug.cgi?id=2466912WEB
- https://github.com/jupyter-server/jupyter_serverPACKAGE
- https://github.com/jupyter-server/jupyter_server/commit/057869a327c46730afede3eab0ca2d2e3e74aceaWEB
- https://github.com/jupyter-server/jupyter_server/commit/49b34392feaa97735b3b777e3baf8f22f2a14ed8WEB
- https://github.com/jupyter-server/jupyter_server/pull/603WEB
- https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-24qx-w28j-9m6pWEB
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