CVE-2026-6657
HighCVSS 8.8Exploitation Probability (EPSS)
Low risk10th percentile - higher than 10% of all known CVEs
Summary
In jupyter-server versions 1.12.0 through 2.17.0, a vulnerability allows bypassing CORS origin validation when using `allow_origin_pat`. The issue is due to `re.match()` only anchoring at the start, allowing attacker-controlled domains like `trusted.example.com.evil.com` to pass validation for patterns intended for `trusted.example.com`. This affects CORS headers, WebSocket connections, referer validation, and login redirects, potentially enabling phishing, arbitrary code execution, and unauthorized access to sensitive API responses.
Risk Assessment
An attacker can conduct phishing attacks, execute arbitrary code, or access sensitive API data, posing a serious security risk to the application.
Recommendation
Update jupyter-server to version 2.17.1 or later, which includes the fix.
Other vulnerabilities in jupyter-server
See all- CVE-2026-86049High
Jupyter Server, the backend for Jupyter web applications, prior to version 2.21.0 copies the Referer header into a JSON header block in the 5xx request logging path without applying the token scrubbing used for the request URI. A request returning HTTP 500 whose Referer contains a token-bearing URL can write that token to server logs in plaintext.
- CVE-2026-44727Medium
Jupyter Server prior to version 2.20 has a stored XSS vulnerability in nbconvert handlers. A notebook with an HTML payload in display_data output can lead to cookie theft, full API access, and kernel RCE.
- CVE-2026-5422High
A path traversal vulnerability in jupyter-server 2.17.0 due to an incorrect root directory boundary check in the _get_os_path() function. This allows unauthorized read/write access to files in sibling directories.
- CVE-2026-40934Medium
Jupyter Server up to version 2.17.0 persists the secret used to sign authentication cookies to a static file and does not rotate it after a password change. After a password reset and server restart, previously issued cookies remain valid, allowing an attacker who captured a session cookie to retain access despite the password change.
- CVE-2026-40110High
Jupyter Server versions 2.17.0 and earlier use re.match() for Origin header validation, allowing bypass of CORS restrictions. An attacker controlling a domain like trusted.example.com.evil.com can make cross-origin requests to the server API.
- CVE-2026-35397High
Jupyter Server versions 2.17.0 and earlier contain a path traversal vulnerability in the REST API that allows an authenticated user to escape the configured root_dir and access sibling directories whose names begin with the same prefix as the root_dir. An attacker can read, write, and delete files in affected sibling directories. Multi-tenant deployments with predictable naming schemes are particularly at risk. Version 2.18.0 contains a fix.
- CVE-2025-61669Medium
Jupyter Server versions through 2.17.0 have insufficient validation of the next query parameter in the login flow within LoginFormHandler._redirect_safe(), allowing redirects to arbitrary external domains. An attacker can use a crafted login URL to redirect users to a malicious site and facilitate phishing attacks.
- CVE-2023-40170Medium
In jupyter-server, improper cross-site credential checks on `/files/` URLs could allow exposure of certain file contents or accessing files when opening untrusted files. This issue has been addressed in version `2.7.2`.
- CVE-2023-39968Medium
The vulnerability in jupyter-server allows for an Open Redirect attack, enabling redirection of users to arbitrary sites after logging into a Jupyter server. Maliciously crafted login links can lead to unauthorized redirects.
Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS