High Cross-site scripting

CVE-2026-40171 — Jupyter Notebook and JupyterLab token theft via stored XSS in help command linker

In Jupyter Notebook versions 7.0.0 through 7.5.5, JupyterLab versions 4.5.6 and earlier, and the corresponding @jupyter-notebook/help-extension and @jupyterlab/help-extension packages before 7.5.6 and 4.5.7, a stored cross-site scripting issue in the help command linker can be chained with attacker-controlled notebook content to steal authentication tokens with a single click. An attacker can craft a malicious notebook file containing elements that appear indistinguishable from legitimate controls and trigger execution when a user interacts with them. Successful exploitation allows theft of the user's authentication token and complete takeover of the Jupyter session through the REST API, including reading files, creating or modifying files, accessing kernels to execute arbitrary code, and creating terminals for shell access. This issue has been fixed in Notebook 7.5.6, JupyterLab 4.5.7, @jupyter-notebook/help-extension 7.5.6, and @jupyterlab/help-extension 4.5.7. As a workaround, disable the affected help extensions or set allowCommandLinker to false in the sanitizer configuration.

Published May 6, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: GitHub_M

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.7% (30-day exploitation probability)+8
Technical severity (high)+6

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.66%

ahead of 51% of scored CVEs · Oct 14, 2026

Affects

Jupyter

Notebook and 2 more

CVSS base

8.4

High · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

None

none · proof-of-concept · active

Automatable

can an attacker script the kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Jupyter Notebook, Jupyter-notebook Help-extension, Jupyterlab Help-extension…).
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Exploitation requires user interaction: tighten email/web filtering and warn affected users.
Search available logs for exploit probes matching the vulnerability class (cross-site scripting), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Jupyter	Notebook	version >=7.0.0, <= 7.5.5	Vulnerable	CVE Program (cve.org) e CISA ADP
Jupyter-notebook	Help-extension	version >=7.0.0,<= 7.5.5	Vulnerable	CVE Program (cve.org) e CISA ADP
Jupyterlab	Help-extension	version <=4.5.6	Vulnerable	CVE Program (cve.org) e CISA ADP
Jupyterlab	Jupyterlab	version <= 4.5.6	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Attack requirements

None

Privileges required

High

User interaction

Active

Scope

Confidentiality (vulnerable system)

High

Integrity (vulnerable system)

High

Availability (vulnerable system)

High

Confidentiality (subsequent)

None

Integrity (subsequent)

None

Availability (subsequent)

None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
8.4	CVSS 4.0	High	—	—	security-advisories@github.com via NIST National Vulnerability Database
8.4	CVSS 4.0	High	—	—	GitHub_M via CVE Program (cve.org) e CISA ADP

CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

(score shown at the top: security-advisories@github.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-79 · Cross-site Scripting (XSS)

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.66%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Monitor CSP violation reports and script payloads in reflected parameters.

web/proxy/WAF logsnetwork IDS/IPSapplication logs

Timeline

What happened to this CVE, newest first.

2026
Affected products added · jupyter/notebook, jupyterlab/help-extension, jupyterlab/jupyterlab, jupyter-notebook/help-extension
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
CVSS changed · 8.4
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Awaiting Analysis
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
May 6, 2026 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

1 on the record

github.com/jupyter/notebook/security/advisories/GHSA-rch3-82jr-f9w9
x_refsource_CONFIRM, NIST National Vulnerability Database

Elsewhere on this site

Jupyter
every CVE for this vendor

Cross-site scripting
same class

CWE-79
other pages naming this weakness

Related CVEs (same products)

Medium CVE-2026-102832 JupyterLab: Command link trust prompt in JupyterLab can trust a document other than the one clicked 2d
Medium CVE-2026-67338 JupyterLab before 4.5.9 Stored XSS via Extension Manager Aug 1, 2026
Critical CVE-2026-42557 jupyterlab: Command linker attributes in HTML enable one-click command execution from untrusted content May 13, 2026
High CVE-2026-42266 JupyterLab has an Extension Manager API/GUI Policy Discrepancy allowing 3rd party (malicious) extensions install via POST request. May 13, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-40171 is "Jupyter Notebook and JupyterLab token theft via stored XSS in help command linker", rated High. It affects Notebook (Jupyter); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 8.4 describes technical severity. EPSS 0.66% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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