Machine-written summary
Summary written by Claude Haiku from the source advisory. Not reviewed by a person.
JupyterHub versions 4.1.0 up to but not including 5.4.5 are affected by a cross-site request forgery flaw in which XSRF protection wrongly treats requests with Sec-Fetch-Mode set to no-cors as same-origin. An attacker can get a logged-in user's browser to submit forms such as spawn and share-acceptance, which can start a server or make a user accept a share giving the attacker's server access; the JSON API is not affected. Upgrade to JupyterHub 5.4.5. If a reverse proxy is in use, configure it to drop requests carrying Sec-Fetch-Mode: no-cors.
Not analysed yet
We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.
Severity and exploitation
| Score | Rating | CVSS | Vector | Source |
|---|---|---|---|---|
| 5.4 | Medium | 3.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L | CNA (GitHub_M) |
- CISA KEV Not listed.
- EPSS 0.0015, the 3rd percentile, on 12 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.
Timeline
- 31 Oct 2026, 14:11 UTC First seen by agentprime
- 31 Oct 2026, 14:11 UTC Confirmed by OSV