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CVE-2026-35397 high CVSS 8.8

Path Traversal in jupyter-server (CVE-2026-35397)

Summary

Path traversal in jupyter-server (CVE-2026-35397). Successful exploitation can lead to full system takeover. Exploitable via root_dir. Mitigation: upgrade to 2.18.0 or later.

Original description

The description as published by the source.

Summary

Jupyter Server <=2.17.0 can access directories sibling to the root directory, if it starts with the root dir's name.

PoC

Minimal:

.
├── test/              <- root directory.
│   └── test.txt
└── testtest/
    └── secret.txt     <- file to exfiltrate that we should not be able to access via API

HOST="http://localhost:8888"
TOKEN=""
SIBLING="testtest"
TARGET="secret.txt"

curl -s -X POST \
  "$HOST/api/contents/%2e%2e/$SIBLING/$TARGET/checkpoints" \
  -H "Authorization: token $TOKEN"

Full PoC by @stef41: https://gist.github.com/Yann-P/66d4982a965dee8fcb8dd89db29e7006

Impact

It is possible for an authenticated user to access content outside the server's root_dir in siblings directories sharing the same prefix as the root_dir. The attacker can escalate access, reading, writing, and deleting from sibling directories.

This can have a tangible impact for deployments using predictable naming scheme with multi-tenant server, for example user1, user2, user3, ..., user10 etc, as user1 could access and modify files of all user10 - user19 and higher.

In a hypothetical system where users can choose a name of their folder, an attacker could choose a single-letter username to gain access to a significant number of sibling directories.

Workarounds

Use folder names that do not overlap.

Acknowledgments

Thank you to @stef41 for providing a useful PoC.

Source: NIST National Vulnerability Database 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-2026-35397 has been found in jupyter-server.
Attackers can target a specific entry point like root_dir over the network to misuse the product.
Successful exploitation can lead to full system takeover. CVSS score: 8.8/10.
What to do: upgrade jupyter-server to 2.18.0 or later.
If unsure, ask your IT team or search "jupyter-server CVE-2026-35397" on the vendor's site.

CVE-2026-35397 (jupyter-server) — CWE-22 / CVSS v3 8.8
Attack vector: remote (network-reachable) / no user interaction
Attack surface: root_dir / user1 / user2 / user3
Patched: 2.18.0 — apply immediately
Workaround: Use folder names that do not overlap.
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.

❓ What is the problem

Path traversal (CWE-22) exists in jupyter-server. Attackers reach the vulnerable code path via root_dir.

📍 Affected scope

Check the vendor advisory for the affected versions of jupyter-server. Attack surface: root_dir / user1 / user2 / user3.

🔥 Severity

Severity: High (CVSS 8.8/10). Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 2.18.0.

🛡️ Workaround

Workaround: Use folder names that do not overlap.

🔍 Detection

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

  1. 1
    Identify 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。

  2. 2
    Apply temporary workaround mitigate 
    Use folder names that do not overlap.

    パッチが適用されるまでの応急処置として、Use folder names that do not overlap. を実施。回避策の副作用 (機能低下) を確認した上で。

  3. 3
    Apply 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。

  4. 4
    Post-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

pip jupyter-server
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.18.0"}]}]
PyPI jupyter-server
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.18.0"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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