CVE-2026-6657: A vulnerability in jupyter-server versions 1.12.0 through 2.17.0 allows an attacker to bypass CORS origin vali

Q: How do I fix CVE-2026-6657?

jupyter server: upgrade to newer than 2.17.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-6657 being exploited?

CVE-2026-6657 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-6657 affect?

CVE-2026-6657 affects jupyter server. Severity is high (CVSS 8.8). A vulnerability in jupyter-server versions 1.12.0 through 2.17.0 allows an attacker to bypass CORS origin validation when the `allow_origin_pat` configuration is used. The issue arises from the use of `re.match()` for validating the `Origin

Q: How urgent is CVE-2026-6657?

Priority 59/100. High severity; EPSS top 7%: very likely to be exploited; Public exploit reference

This month

HIGH 8.8UPGRADE

CVE-2026-6657 is a high-severity flaw (CVSS 8.8) affecting jupyter server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A vulnerability in jupyter-server versions 1.12.0 through 2.17.0 allows an attacker to bypass CORS origin validation when the `allow_origin_pat` configuration is used. The issue arises from the use of `re.match()` for validating the `Origin` header, which only anchors at the start of the string. This allows attacker-controlled domains such as `trusted.example.com.evil.com` to pass validation against patterns intended to match `trusted.example.com

Why this priority

High severity
EPSS top 7%: very likely to be exploited
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	6.2% (top 7%)
CISA exploited list	No
Weakness	CWE-346
Published	2026-06-03
Last modified	2026-07-21

Publisher (CNA): huntr.dev · Vendor: jupyter

Last updated 2026-07-21 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-03 16:16 UTCPublished CVE record published
2026-07-21 19:10 UTCUpdated Record last modified

jupyter jupyter server UPGRADE

Affected: >= 1.12.0 and <= 2.17.0

Fixed in: newer than 2.17.0

Safe to downgrade to: a release before 1.12.0

1. Check installed version

apt-cache policy jupyter-server || rpm -q jupyter-server || jupyter-server --version

2. UPGRADE to newer than 2.17.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade jupyter-server

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade jupyter-server

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 1.12.0 (Debian / Ubuntu)

apt-cache madison jupyter-server sudo apt install jupyter-server=<VERSION_BEFORE_1.12.0> sudo apt-mark hold jupyter-server

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

dnf --showduplicates list jupyter-server sudo dnf downgrade jupyter-server-<VERSION_BEFORE_1.12.0> sudo dnf versionlock add jupyter-server

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.

Exact fixes by distribution

Python (pip) · jupyter-server · NO FIX YET · vulnerable: >= 1.12.0, <= 2.17.0 · source

Fedora 46 · arm-none-eabi-binutils-cs · FIXED · 2.47-1.fc46 · FEDORA-2026-7498616952 · source

sudo dnf upgrade --advisory=FEDORA-2026-7498616952

Debian 12 · jupyter-server · NO FIX YET

Debian 13 · jupyter-server · NO FIX YET

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-2026-6657?

jupyter server: upgrade to newer than 2.17.0. Exact commands for each OS are on this page.

Is CVE-2026-6657 being exploited?

CVE-2026-6657 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-2026-6657 affect?

CVE-2026-6657 affects jupyter server. Severity is high (CVSS 8.8). A vulnerability in jupyter-server versions 1.12.0 through 2.17.0 allows an attacker to bypass CORS origin validation when the `allow_origin_pat` configuration is used. The issue arises from the use of `re.match()` for validating the `Origin

How urgent is CVE-2026-6657?

Priority 59/100. High severity; EPSS top 7%: very likely to be exploited; Public exploit reference

Software pages

Jupyter vulnerabilities

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References

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