# What is CVE-2020-26275? > CVE-2020-26275 is a medium-severity flaw (CVSS 6.1) in Jupyter Server, published on 21 December 2020. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 1.4%. If you run an affected version, plan in the vendor’s fix. Canonical page: https://www.precursorintelligence.com/what-is/cve-2020-26275 ## At a glance - **Verdict:** Plan it in. No sign of exploitation and a low forecast. Patch it in your normal update cycle. - **Precursor Intelligence risk score:** 45 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes. - **Severity:** Medium (CVSS 6.1 out of 10) - **Known to be exploited:** No, not on the list of flaws known to be exploited today - **Chance of use in the next 30 days:** 1.4% (latest exploit-likelihood forecast) - **Published:** 21 December 2020 - **Record last updated:** 6 August 2022 - **Main product:** Jupyter Server - **Affected products:** 1 ## What is CVE-2020-26275? In plain terms It can be attacked from anywhere on the internet without logging in, but a person has to take an action first. If it works, the attacker can read some data and change some data. ### The official description The Jupyter Server provides the backend (i.e. the core services, APIs, and REST endpoints) for Jupyter web applications like Jupyter notebook, JupyterLab, and Voila. In Jupyter Server before version 1.1.1, an open redirect vulnerability could cause the jupyter server to redirect the browser to a different malicious website. All jupyter servers running without a base_url prefix are technically affected, however, these maliciously crafted links can only be reasonably made for known jupyter server hosts. A link to your jupyter server may *appear* safe, but ultimately redirect to a spoofed server on the public internet. This same vulnerability was patched in upstream notebook v5.7.8. This is fixed in jupyter_server 1.1.1. If upgrade is not available, a workaround can be to run your server on a url prefix: "jupyter server --ServerApp.base_url=/jupyter/". ### What kind of flaw is it? - CWE-601: URL Redirection to Untrusted Site ('Open Redirect') ### How an attack on it works - Where an attacker can be: Anywhere on the internet - How hard it is to pull off: Easy: no special conditions - Login needed first: No login needed - Does someone have to click: Yes, a person has to take an action - What an attacker gets: Can read some data and change some data Severity vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N` ## Is CVE-2020-26275 being exploited? Not that we know of It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 1.4%. That can change at any time, which is why we keep watching. Exploit likelihood over the last 7 days: 1.4%, 1.4%, 1.4%, 1.4%, 1.4%, 1.4%, 1.4%. ### Timeline - 21 December 2020: Published - 6 August 2022: Record last updated ### How Precursor Intelligence ranks it CVE-2020-26275 scores **45 out of 100 (Medium)**, with the action "Plan remediation". Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less: - Evidence it is being exploited: biggest factor - How severe it is: strong factor - How widely exposed it is: smaller factor - Threat activity around it: smaller factor 85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it. ## Who is affected by CVE-2020-26275? The published record lists 1 product. Versions are as published: "before 1.1.1" means every version up to, but not including, 1.1.1. - [Jupyter Server](https://www.precursorintelligence.com/product/jupyter/jupyter_server) by [Jupyter](https://www.precursorintelligence.com/vendors/jupyter) (Application): before 1.1.1 ## How do I fix CVE-2020-26275? 1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list. 2. **Apply the vendor’s fix.** Install the update named in the vendor’s advisory. We’ve put the advisories and patch notes first in the list. 3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in. 4. **Keep an eye on it.** Track the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood. ### References - [github.com](https://github.com/jupyter-server/jupyter_server/commit/85e4abccf6ea9321d29153f73b0bd72ccb3a6bca) (Patch, Third-party advisory) - [github.com](https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-9f66-54xg-pc2c) (Patch, Third-party advisory) - [advisory.checkmarx.net](https://advisory.checkmarx.net/advisory/CX-2020-4291) (Exploit, Third-party advisory) - [pypi.org](https://pypi.org/project/jupyter-server/) (Product) ## Questions ### What is CVE-2020-26275? CVE-2020-26275 is a medium-severity flaw in Jupyter Server, published on 21 December 2020. It can be attacked from anywhere on the internet without logging in, but a person has to take an action first. If it works, the attacker can read some data and change some data. ### How serious is CVE-2020-26275? It scores 6.1 out of 10 on the CVSS severity scale, which is medium. Our risk score for CVE-2020-26275 is 45 out of 100, which is Medium. Its action is "Plan remediation". No sign of exploitation and a low forecast. Patch it in your normal update cycle. ### Is CVE-2020-26275 being exploited? It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 1.4%. That can change at any time, which is why we keep watching. ### Which versions does CVE-2020-26275 affect? For Jupyter Server: before 1.1.1. ### How do I fix CVE-2020-26275? Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet. ## Does CVE-2020-26275 affect you? Precursor Intelligence keeps checking for you: - **Tell us what you run.** Pick your software from a list, or let us work it out from your website. - **We match it to every flaw.** Over 400,000 published flaws, checked against your list. - **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it. - **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools. Start free (no card, nothing to install): https://www.precursorintelligence.com/register Book a demo: https://www.precursorintelligence.com/contact