How severe is CVE-2026-40934?

CVE-2026-40934 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over network with high attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-40934 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (23rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-40934?

CVE-2026-40934 affects Jupyter Jupyter Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-40934?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-40934 have an EU (EUVD) identifier?

Yes. CVE-2026-40934 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-27513.

When was CVE-2026-40934 published?

CVE-2026-40934 was published on 2026-05-05 and last updated on 2026-06-17.

CVE-2026-40934

CVE-2026-40934 is a medium-severity vulnerability in Jupyter Jupyter Server with a CVSS 3.x base score of 6.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-613.

Key facts

Severity: Medium (CVSS 3.x base score 6.8)
CVSS v4: 7.6
EPSS exploit prediction: 0% (23rd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-27513
Weakness: CWE-613
Affected product: Jupyter Jupyter Server
Published: 2026-05-05
Last modified: 2026-06-17

Description

Jupyter Server is the backend for Jupyter web applications. In versions 2.17.0 and earlier, the secret used to sign authentication cookies is persisted to a static file at ~/.local/share/jupyter/runtime/jupyter_cookie_secret and is never rotated when a user changes their password. After a password reset and server restart, any previously issued authentication cookie remains cryptographically valid because the signing key has not changed. An attacker who has captured a session cookie through any means retains full authenticated access to the server regardless of subsequent password changes. This affects deployments using password-based authentication, particularly shared or public-facing servers where credential rotation is expected to revoke existing sessions. This issue has been fixed in version 2.18.0.

Frequently asked questions

What is CVE-2026-40934?: Jupyter Server is the backend for Jupyter web applications. In versions 2.17.0 and earlier, the secret used to sign authentication cookies is persisted to a static file at ~/.local/share/jupyter/runtime/jupyter_cookie_secret and is never rotated when a user changes their password. After a password reset and server restart, any previously issued authentication cookie remains cryptographically valid because the signing key has not changed. An attacker who has captured a session cookie through any means retains full authenticated access to the server regardless of subsequent password changes. This affects deployments using password-based authentication, particularly shared or public-facing servers where credential rotation is expected to revoke existing sessions. This issue has been fixed in version 2.18.0.
How severe is CVE-2026-40934?: CVE-2026-40934 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over network with high attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-40934 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (23rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-40934?: CVE-2026-40934 affects Jupyter Jupyter Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-40934?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-40934 have an EU (EUVD) identifier?: Yes. CVE-2026-40934 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-27513.
When was CVE-2026-40934 published?: CVE-2026-40934 was published on 2026-05-05 and last updated on 2026-06-17.

References

https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-5mrq-x3x5-8v8f

Affected products (1)

cpe:2.3:a:jupyter:jupyter_server:*:*:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

129.212.181.245 (ipv4-addr)