Cross site scripting (XSS) in JupyterHub via Self-XSS leveraged by Cookie Tossing

### Impact Affected configurations: - Single-origin JupyterHub deployments - JupyterHub deployments with user-controlled applications running on subdomains or peer subdomains of either the Hub or a single-user server. By tricking a user into visiting a malicious subdomain, the attacker can achieve an XSS directly affecting the former's session. More precisely, in the context of JupyterHub, this XSS could achieve the following: - Full access to JupyterHub API and user's single-user server, e.g. - Create and exfiltrate an API Token - Exfiltrate all files hosted on the user's single-user server: notebooks, images, etc. - Install malicious extensions. They can be used as a backdoor to silently regain access to victim's session anytime. ### Patches To prevent cookie-tossing: - Upgrade to JupyterHub 4.1 (both hub and user environment) - enable per-user domains via `c.JupyterHub.subdomain_host = "https://mydomain.example.org"` - set `c.JupyterHub.cookie_host_prefix_enabled = True` to enable domain-locked cookies or, if available (applies to earlier JupyterHub versions): - deploy jupyterhub on its own domain, not shared with any other services - enable per-user domains via `c.JupyterHub.subdomain_host = "https://mydomain.example.org"`

CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

Severity from

GitHub (reviewed advisory)

Weakness

CWE-352, CWE-565, CWE-79

Also known as

BIT-jupyterhub-2024-28233, CVE-2024-28233, PYSEC-2026-1480

• github.com/jupyterhub/jupyterhub/security/advisories/GHSA-7r3h-4ph8-w38g
• nvd.nist.gov/vuln/detail/CVE-2024-28233
• github.com/jupyterhub/jupyterhub/commit/e2798a088f5ad45340fe79cdf1386198e664f77f
• github.com/jupyterhub/jupyterhub