The flaw is a CORS origin‑validation bypass that occurs when jupyter‑server uses the allow_origin_pat configuration. The underlying weakness is CWE‑346: trusted content perceived equivocation, because re.match() only anchors at the start of the string, permitting attacker‑controlled domains such as trusted.example.com.evil.com to pass the check intended for trusted.example.com. This allows malicious sites to craft Origin headers that the server accepts, enabling phishing, unauthorized API access, and potentially triggering arbitrary code execution through cross‑site request forgery or other downstream logic.

All Ubuntu, Windows, macOS or other platforms that run jupyter‑server versions 1.12.0 through 2.17.0 are affected. The vulnerability concerns the Jupyter team’s jupyter‑server package; no specific operating system restrictions apply beyond normal deployment environments.

The CVSS score of 6.1 indicates medium severity, but the lack of available EPSS data means the exploitation probability is unknown. The vulnerability is not listed in CISA’s KEV catalog. The likely attack vector is remote HTTP or WebSocket requests that set a malicious Origin header; any external domain can exploit the bug by sending crafted requests that satisfy the allow_origin_pat regex. If unmitigated, attackers could conduct phishing campaigns, retrieve sensitive API data, or exploit downstream execution paths that depend on trusted origins.