Jupyter Server Proxy has a reflected XSS issue in host parameter

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2024-35225: 0.45% estimated exploitation activity in the next 30 days; percentile 38.85 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

11 Jun 2024, 21:12 UTC

Last modified by the source

10 Jun 2026, 17:14 UTC

Source last checked

26 Oct 2026, 13:31 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-fvcq-4x64-hqxr

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-fvcq-4x64-hqxr

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# Patch Next advisory brief: CVE-2024-35225

Advisory: Jupyter Server Proxy has a reflected XSS issue in host parameter
IDs: CVE-2024-35225, GHSA-fvcq-4x64-hqxr
Record: https://patchnext.com/advisories/cve-2024-35225 (revision 2, source checked 26 Oct 2026, 13:31 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: jupyter-server-proxy 4.2.0, 3.2.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI jupyter-server-proxy: affected >= 3.0.0, < 3.2.4; >= 4.0.0, < 4.2.0; fixed in 4.2.0, 3.2.4

## Suggested inspection (read-only)
- `python -m pip show jupyter-server-proxy`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on jupyter-server-proxy.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-fvcq-4x64-hqxr (OSV record GHSA-fvcq-4x64-hqxr lists affected ranges: PyPI jupyter-server-proxy >=3.0.0 =4.0.0 <4.2.0 (fixed))
- Verified: https://github.com/advisories/GHSA-fvcq-4x64-hqxr (GitHub-reviewed advisory GHSA-fvcq-4x64-hqxr lists affected ranges: PyPI jupyter-server-proxy >=3.0.0 =4.0.0 <4.2.0)

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