---
title: "CVE-2024-35225: Jupyter Server Proxy has a reflected XSS issue in host parameter"
url: https://erroneo.us/security/cve/CVE-2024-35225/
description: "CVE-2024-35225 (jupyter-server-proxy (PyPI)): Jupyter Server Proxy allows users to run arbitrary external processes alongside their notebook server and…"
type: vulnerability-record
section: "Security Digest"
date_published: 2024-06-11
date_modified: 2025-02-28
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2024-35225"
kev: false
cvss: 9.7
epss: 0.00446
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2024-35225: Jupyter Server Proxy has a reflected XSS issue in host parameter

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.4% , percentile 38: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 38% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Needs a user to click or open something. Phishing makes that realistic, but it is not wormable.
- Only applies if your dependency tree includes jupyter-server-proxy (PyPI) >= 3.0.0, < 3.2.4, fixed in 3.2.4 ; jupyter-server-proxy (PyPI) >= 4.0.0, < 4.2.0, fixed in 4.2.0 . Check your lockfile, including transitive dependencies.

## What it is

Jupyter Server Proxy allows users to run arbitrary external processes alongside their notebook server and provide authenticated web access to them. Versions of 3.x prior to 3.2.4 and 4.x prior to 4.2.0 have a reflected cross-site scripting (XSS) issue. The /proxy endpoint accepts a host path segment in the format /proxy/ . 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/ , 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. Patches are included in versions 4.2.0 and 3.2.4. As a workaround, server operators who are unable to upgrade can disable the jupyter-server-proxy extension.

## Affected packages

- PyPI `jupyter-server-proxy` >= 3.0.0, < 3.2.4 → fixed: 3.2.4
- PyPI `jupyter-server-proxy` >= 4.0.0, < 4.2.0 → fixed: 4.2.0

## Affected products (CVE record)

- jupyterhub jupyter-server-proxy: >= 3.0.0, < 3.2.4, >= 4.0.0, < 4.2.0

## Severity

- GitHub_M CVSS 3.1: 9.7 `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H`
- GitHub CVSS 3.1: 9.6 `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.45% probability of exploitation activity in the next 30 days; percentile 38.

## Sources

- [GitHub Advisory GHSA-fvcq-4x64-hqxr](https://github.com/advisories/GHSA-fvcq-4x64-hqxr)
- [CVE.org record CVE-2024-35225](https://www.cve.org/CVERecord?id=CVE-2024-35225)
- [NVD entry CVE-2024-35225](https://nvd.nist.gov/vuln/detail/CVE-2024-35225)
- [github.com](https://github.com/jupyterhub/jupyter-server-proxy/security/advisories/GHSA-fvcq-4x64-hqxr)
- [github.com](https://github.com/jupyterhub/jupyter-server-proxy/commit/7abc9dc5bbb0b4b440548a5375261b8b8192fc22)
- [github.com](https://github.com/jupyterhub/jupyter-server-proxy/commit/ff78128087e73fb9d0909e1366f8bf051e8ea878)
- [github.com](https://github.com/jupyterhub/jupyter-server-proxy/blob/62a290f08750f7ae55a0c29ca339c9a39a7b2a7b/jupyter_server_proxy/handlers.py#L328)
- [github.com](https://github.com/pypa/advisory-database/tree/main/vulns/jupyter-server-proxy/PYSEC-2024-236.yaml)

---
Source page: https://erroneo.us/security/cve/CVE-2024-35225/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt