CVE-2026-40110High▾ TwilightJupyter Server has a CORS Origin Validation Bypass via `re.match()` in `allow_origin_pat`
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 41.3 · likelihood 0.1 · exploitation 0
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Exploit-prediction probability, daily snapshots since Jul 13.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via OSV
0.3%
0.3% → 0.3%
Last analysed / modified upstream
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
jupyter-server < 2.18.0Upgrade to a patched release:
jupyter-server 2.18.0Connected by shared product, vendor, weakness, or advisory.
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