CVE-2026-40864: JupyterHub is software that allows users to create a multi-user server for Jupyter notebooks

Routine

MEDIUM 5.4UPGRADE

CVE-2026-40864 is a medium-severity flaw (CVSS 5.4) affecting jupyterhub. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

JupyterHub is software that allows users to create a multi-user server for Jupyter notebooks. In versions 4.1.0 through 5.4.4, XSRF protection (updated in 4.1.0) inappropriately treated requests with Sec-Fetch-Mode: no-cors as same-origin requests, 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

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	5.4 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.1% (top 96%)
CISA exploited list	No
Weakness	CWE-352
Published	2026-05-22
Last modified	2026-07-23

Publisher (CNA): GitHub, Inc. · Vendor: jupyter

Last updated 2026-07-23 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-22 21:16 UTCPublished CVE record published
2026-07-23 11:10 UTCUpdated Record last modified

jupyter jupyterhub UPGRADE

Affected: >= 4.1.0 and < 5.4.5

Fixed in: 5.4.5

Safe to downgrade to: a release before 4.1.0

1. Check installed version

apt-cache policy jupyterhub || rpm -q jupyterhub || jupyterhub --version

2. UPGRADE to 5.4.5 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade jupyterhub

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade jupyterhub

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 4.1.0 (Debian / Ubuntu)

apt-cache madison jupyterhub sudo apt install jupyterhub=<VERSION_BEFORE_4.1.0> sudo apt-mark hold jupyterhub

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list jupyterhub sudo dnf downgrade jupyterhub-<VERSION_BEFORE_4.1.0> sudo dnf versionlock add jupyterhub

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-40864?

jupyterhub: upgrade to 5.4.5. Exact commands for each OS are on this page.

Is CVE-2026-40864 being exploited?

CVE-2026-40864 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-40864 affect?

CVE-2026-40864 affects jupyterhub. Severity is medium (CVSS 5.4). JupyterHub is software that allows users to create a multi-user server for Jupyter notebooks. In versions 4.1.0 through 5.4.4, XSRF protection (updated in 4.1.0) inappropriately treated requests with Sec-Fetch-Mode: no-cors as same-origin r

How urgent is CVE-2026-40864?

Priority 20/100. No elevated risk signals yet.

Software pages

Jupyter vulnerabilities

Related CVEs

CVE-2026-33709 MEDIUM 6.1 UPGRADE JupyterHub is software that allows one to create a multi-user server for Jupyter notebooks

References

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