Vulnerability in jupyter-server (CVE-2026-40934)
Summary
Vulnerability in jupyter-server (CVE-2026-40934). Confidential information can be exposed externally. Mitigation: upgrade to 2.18.0 or later.
Original description
The description as published by the source.
Summary
A persistent cookie secret vulnerability allows authenticated users to maintain indefinite access even after password changes.
The cookie secret used to sign authentication cookies is stored in a permanent file (~/.local/share/jupyter/runtime/jupyter_cookie_secret) that is never automatically rotated or cleared, allowing stolen or compromised cookies to remain valid indefinitely regardless of password resets.
PoC
- Start a Jupyter server with password authentication:
jupyter server password,jupyter server - Log in with the password and capture the authentication cookie (e.g., just login with a browser).
- Change the password to revoke access:
jupyter server password - Restart the server
- Use the old stolen cookie => remains valid and provides full authenticated access.
Impact
- All jupyter-server deployments using password authentication where security incidents may occur
- Multi-user systems where one user's compromised session should be revocable by administrators
- Shared or public-facing Jupyter servers where credential rotation is a security requirement
- Any deployment where password changes are expected to revoke existing sessions
Patches
Jupyter Server 2.18+
Workaround
rm ~/.local/share/jupyter/runtime/jupyter_cookie_secret
# Then restart the server
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-40934 has been found in jupyter-server.
Confidential information can be exposed externally. CVSS score: 6.8/10.
What to do: upgrade jupyter-server to 2.18.0 or later.
If unsure, ask your IT team or search "jupyter-server CVE-2026-40934" on the vendor's site.
CVE-2026-40934 (jupyter-server) — CWE-613 / CVSS v3 6.8
Attack vector: remote (network-reachable) / no user interaction
Patched: 2.18.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-613) exists in jupyter-server.
Check the vendor advisory for the affected versions of jupyter-server.
Severity: Medium (CVSS 6.8/10). Confidential information can be exposed externally.
Update to 2.18.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'jupyter-server' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'jupyter-server' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
jupyter-serverを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade jupyter-server to 2.18.0ステージング環境で 2.18.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-40934 jupyter-server
- Ubuntu UBUNTU-CVE-2026-40934 jupyter-server
References
- advisory nvd.nist.gov
- exploit security-advisories@github.com
- package github.com
- web github.com
- web github.com