CVE-2024-35225 is a critical-severity (CVSS 9.6) Cross-site Scripting (XSS) vulnerability in jupyter-server-proxy. A fix is available for jupyter-server-proxy — see the affected versions and patch details below.
Jupyter Server Proxy has a reflected XSS issue in host parameter
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2024-35225.
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.
How urgent is this, really
CVE-2024-35225 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
jupyter-server-proxy🐍jupyter-server-proxyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Impact
There is a reflected cross-site scripting (XSS) issue in jupyter-server-proxy[1]. The /proxy endpoint accepts a host path segment in the format /proxy/<host>. When this endpoint is called with an invalid host value, jupyter-server-proxy replies with a response that includes the value of host, without sanitization [2]. A third-party actor can leverage this by sending a phishing link with an invalid host value containing custom JavaScript to a user. When the user clicks this phishing link, the browser renders the response of GET /proxy/<host>, which runs the custom JavaScript contained in host set by the actor.
As any arbitrary JavaScript can be run after the user clicks on a phishing link, this issue permits extensive access to the user's JupyterLab instance for an actor. This issue exists in the latest release of jupyter-server-proxy, currently v4.1.2.
Impacted versions: >=3.0.0,<=4.1.2
Patches
The patches are included in ==4.2.0 and ==3.2.4.
Workarounds
Server operators who are unable to upgrade can disable the jupyter-server-proxy extension with:
jupyter server extension disable jupyter-server-proxy
References
[1] : https://github.com/jupyterhub/jupyter-server-proxy/ [2] : https://github.com/jupyterhub/jupyter-server-proxy/blob/62a290f08750f7ae55a0c29ca339c9a39a7b2a7b/jupyter_server_proxy/handlers.py#L328
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | jupyter-server-proxy | ≥ 3.0.0&&< 3.2.4 | 3.2.4pip install --upgrade 'jupyter-server-proxy==3.2.4' |
| 🐍PyPI | jupyter-server-proxy | ≥ 4.0.0&&< 4.2.0 | 4.2.0pip install --upgrade 'jupyter-server-proxy==4.2.0' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for jupyter-server-proxy, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update jupyter-server-proxy to 3.2.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-35225 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2024-35225 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2024-35225. 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-2024-35225 in your dependencies?
O3 Security finds CVE-2024-35225 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.