Vulnerability in jupyter_server (CVE-2026-86049)
Summary
Vulnerability in jupyter_server (CVE-2026-86049). Successful exploitation can lead to full system takeover. Exploitable via POST /api/kernels. Mitigation: upgrade to 2.21.0 or later.
Original description
The description as published by the source.
Summary
When a request returns a 500, jupyter_server/log.py logs a small JSON block of request headers.
The Referer header was copied into it as-is, so a token in the Referer URL ended up in the logs in plain text.
Impact
Anyone who can read the server logs can pick tokens out of these 500 entries. Tokens end up in the Referer during normal token-based login and launch flows.
Affected: all versions before 2.21.0.
PoC
Any malformed request that returns a 500 works:
curl -i -X POST \
-H 'Content-Type: application/json' \
-H 'Referer: http://127.0.0.1:8899/tree?token=REFERTOKEN' \
--data '{"name":123}' \
'http://127.0.0.1:8899/api/kernels?token=VALIDTOKEN'
The log shows the token twice, once raw and once redacted:
"Referer": "http://127.0.0.1:8899/tree?token=REFERTOKEN",
[E ... ServerApp] 500 POST /api/kernels?token=[secret] (...) referer=http://127.0.0.1:8899/tree?token=[secret]
Patches
Fixed in 2.21.0 by 5251352. Header values are now scrubbed before the block is logged. Upgrade to 2.21.0 or later.
Workarounds
Limit who can read the server logs. If you can, avoid flows that put the token in the URL.
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-2026-86049 has been found in jupyter_server.
Attackers can target a specific entry point like POST /api/kernels over the network to misuse the product.
Successful exploitation can lead to full system takeover. CVSS score: 7.1/10.
What to do: upgrade jupyter_server to 2.21.0 or later.
If unsure, ask your IT team or search "jupyter_server CVE-2026-86049" on the vendor's site.
CVE-2026-86049 (jupyter_server) — CWE-532 / CVSS v3 7.1
Attack vector: remote (network-reachable)
Attack surface: POST /api/kernels / Referer header
Patched: 2.21.0 — apply immediately
Workaround: Limit who can read the server logs.
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-532) exists in jupyter_server. Attackers reach the vulnerable code path via POST /api/kernels.
Check the vendor advisory for the affected versions of jupyter_server. Attack surface: POST /api/kernels / Referer header.
Severity: High (CVSS 7.1/10). Successful exploitation can lead to full system takeover.
Update to 2.21.0.
Workaround: Limit who can read the server logs.
Search webserver/proxy logs for unusual POST /api/kernels requests with malformed payloads or SQL meta-characters. 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。 -
2Hunt for indicators of compromise detect
grep 'POST /api/kernels' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'アクセスログで
POST /api/kernelsへの異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。 -
3Apply temporary workaround mitigate
Limit who can read the server logs.パッチが適用されるまでの応急処置として、Limit who can read the server logs. を実施。回避策の副作用 (機能低下) を確認した上で。
-
4Apply patch patch
Upgrade jupyter_server to 2.21.0ステージング環境で 2.21.0 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と、Step 2 で見つけた異常検知の続報チェックを含めること。
-
5Post-deployment verification verify
Replay attack against POST /api/kernels on staging to confirm patch closes the vector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 Step 2 と同じログクエリ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-2026-86049 jupyter-server
References
- advisory github.com
- advisory nvd.nist.gov
- package github.com
- package pypi.org
- web github.com
- web github.com
- web github.com
- web github.com