CVE-2026-44727
MediumCVSS 5.4Exploitation Probability (EPSS)
Low risk36th percentile - higher than 36% of all known CVEs
Summary
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.
Risk Assessment
An attacker can steal credentials, manipulate notebooks, or gain remote code execution in the Jupyter kernel, potentially leading to full server compromise.
Recommendation
Immediately update Jupyter Server to version 2.20 or later, which includes a fix for this vulnerability.
Other vulnerabilities in Jupyter Server
See all- CVE-2026-6657High
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.
- 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-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)
Jupyter Server is the backend for Jupyter web applications. Prior to 2.20, the nbconvert HTTP handlers in jupyter_server render user-authored notebook HTML under the Jupyter origin without a sandbox directive in their Content-Security-Policy. Combined with nbconvert.HTMLExporter's default non-sanitizing behavior, a notebook carrying an HTML payload in a display_data output triggers stored XSS with cookie access, full /api/* authority, and kernel RCE. This vulnerability is fixed in 2.20.