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.
<=2.17.0
057869a327c46730afede3eab0ca2d2e3e74acea, 49b34392feaa97735b3b777e3baf8f22f2a14ed8
Wrap your allow_origin_pat value with ^ and $
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
{
"cwe_ids": [
"CWE-625",
"CWE-777"
],
"github_reviewed": true,
"github_reviewed_at": "2026-05-05T16:54:31Z",
"nvd_published_at": "2026-05-05T22:16:00Z",
"severity": "HIGH"
}