---
id: CVE-2026-40864
aliases:
  - GHSA-m68r-v472-jgq9
  - BIT-jupyterhub-2026-40864
  - PYSEC-2026-2189
title: JupyterHub has cross-origin form POSTs bypass XSRF (CWE-352)
summary: JupyterHub has cross-origin form POSTs bypass XSRF (CWE-352)
severity: medium
cvss: 5.4
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L'
vendor: jupyterhub
product: jupyterhub
ecosystem: pip
affected:
  - 'jupyterhub >= 4.1.0, < 5.4.5'
patched:
  - jupyterhub 5.4.5
published: '2026-05-05'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:51:06.307577438Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-m68r-v472-jgq9'
references:
  - url: >-
      https://github.com/jupyterhub/jupyterhub/security/advisories/GHSA-m68r-v472-jgq9
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-40864'
  - url: >-
      https://github.com/jupyterhub/jupyterhub/commit/9c5ec277d3cda5a59de2d8c8117efa77bd941127
  - url: 'https://github.com/jupyterhub/jupyterhub'
tags:
  - osv
  - pip
  - exploit-available
epss: 0.00179
epssPercentile: 0.06674
exploits:
  github: 1
  githubRepos:
    - 'https://github.com/romain-deperne/CVE-2026-40864'
  checkedAt: '2026-09-26T09:05:43.396Z'
exploitAvailable: true
ingestedAt: '2026-07-13T18:58:00.344Z'
---

## Overview

## Summary

JupyterHub's XSRF protection (updated in 4.1.0) inappropriately treated requests with `Sec-Fetch-Mode: no-cors` as same-origin requests, which they are not, bypassing XSRF checks. The JSON API is not affected, only HTTP form endpoints, such as `/hub/spawn` and `/hub/accept-share`, meaning attackers could trigger server spawn (but not access the server) and if the attacker is a JupyterHub user permitted to share access to their server, cause a user to accept a share and have access to the attacker's server.

## Patches

Upgrade to JupyterHub 5.4.5.

## Mitigations

If a reverse proxy is in use, drop requests to JupyterHub with `Sec-Fetch-Mode: no-cors`.

## Affected packages

- `jupyterhub >= 4.1.0, < 5.4.5`

## Remediation

Upgrade to a patched release:

- `jupyterhub 5.4.5`