CVE-2026-6657
HIGHA vulnerability in jupyter-server versions 1.12.0 through 2.17.0 allows an attacker to bypass CORS origin validation when the `allow_origin_pat` configuration is used. The issue arises…
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Description
A vulnerability in jupyter-server versions 1.12.0 through 2.17.0 allows an attacker to bypass CORS origin validation when the allow_origin_pat configuration is used. The issue arises from the use of re.match() for validating the Origin header, which only anchors at the start of the string. This allows attacker-controlled domains such as trusted.example.com.evil.com to pass validation against patterns intended to match trusted.example.com. The vulnerability affects multiple locations in the codebase, including CORS headers, WebSocket connections, referer validation, and login redirects, potentially enabling phishing attacks, arbitrary code execution, and unauthorized access to sensitive API responses.
Affected Products
jupyter serverjupyterDetection & mitigation playbook
Vendor / applianceDetect
Inventory every jupyter jupyter server deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for remote code execution at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.
Remediation status
No patch has shipped for CVE-2026-6657 yet — track the jupyter jupyter server advisory for a fixed release and apply the workarounds below in the meantime.
Mitigate without a patch
Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.
How O3 protects you
O3 detects and blocks CVE-2026-6657 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.
Tailored to CVE-2026-6657. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-6657 being exploited in your environment?
O3's eBPF runtime sensors and L7 egress monitoring detect and block the CVE-2026-6657 exploit chain at execution — protecting unpatched and end-of-life systems until the vendor patch is applied.