CVE-2026-40934Public exploitNetwork attack vector

Persistent authenticated access via unrotated cookie secret

Published May 5, 2026 · Updated May 5, 2026

Insufficient session expiration in Jupyter Server 2.17.0 and earlier allows remote authenticated users to retain full server access. The server persists its authentication-cookie signing secret in a static file and fails to rotate or derive it from changed password credentials. Exploitation requires a previously captured valid cookie and password-based authentication; reuse after a password change and restart preserves authenticated access.

CVSS severity7.6
High
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Insufficient session expiration in Jupyter Server 2.17.0 and earlier allows remote authenticated users to retain full server access. The server persists its authentication-cookie signing secret in a static file and fails to rotate or derive it from changed password credentials. Exploitation requires a previously captured valid cookie and password-based authentication; reuse after a password change and restart preserves authenticated access.

The record

CVE
CVE-2026-40934
Published
May 5, 2026
Updated
May 5, 2026
Vendor
Project Jupyter
Product
Jupyter Server
Classifications
CWE-613, T1550.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 5, 2026CVE publishedPublication date reported by the CVE source.
  2. May 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.18.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Project Jupyter · Jupyter Serverversion=< 2.18.0

Published CVSS scores

7.6GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
6.8NIST NVDCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-613Insufficient Session Expiration
T1550.004Web Session Cookie

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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