Jupyter Server has a CORS Origin Validation Bypass via `re.match()` in `allow_origin_pat` (from huntr)
Date: 2026-05
Affected: pip/jupyter-server
Attack vector: other
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2026-40110
CWE: CWE-777

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


Mitigations:

Architectural layers (MAESTRO):