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

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• 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.

From the GitHub advisory

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/ . 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. This issue exists in the latest release of jupyter-server-proxy, currently v4.1.2. Impacted versions: >=3.0.0,

Patches

The patches are included in ==4.2.0 and ==3.2.4.

Workarounds

Weakness type: CWE-79, CWE-116.

Product: jupyter-server-proxy (PyPI) · Assigned by: GitHub_M · Published: 2024-06-11

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: required (a user must click/open something)
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• 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.

Timeline

• 2024-06-11 — CVE record published by GitHub_M
• 2024-06-11 — GitHub-reviewed advisory GHSA-fvcq-4x64-hqxr published (critical)
• 2024-08-02 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-fvcq-4x64-hqxr github.com
2. CVE.org record CVE-2024-35225 cve.org
3. NVD entry CVE-2024-35225 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com
5. github.com github.com

Critical PyPI advisories · Today’s Security Digest