CVE-2026-6657
HIGHEPSS 92th pctlDescription
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.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Exploit Intelligence
High risk: more likely to be exploited than 92% of all known CVEs.
References
Related Vulnerabilities
Other CWE-346 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2025-34291 | High | 8.8 | 93% | KEV | - |
| CVE-2009-1185 | High | 7.2 | 81% | - | Fix |
| CVE-2020-16952 | High | 8.6 | 71% | - | - |
| CVE-2023-29711 | Critical | 9.8 | 70% | - | - |
| CVE-2015-4495 | High | 8.8 | 69% | KEV | Fix |
| CVE-2024-23898 | High | 8.8 | 67% | - | Fix |
Common questions
How do I fix CVE-2026-6657?
No published fix for CVE-2026-6657 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-6657 being actively exploited?
Not that we know of. CVE-2026-6657 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 5.2% is the estimated probability that it will be exploited in the next 30 days. That is higher than 92% of all scored CVEs.
How severe is CVE-2026-6657?
CVE-2026-6657 has a CVSS v3 base score of 8.8, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-07-21.