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CVE-2026-44727 medium CVSS 5.4

Cross-Site Scripting (XSS) in jupyter-server (CVE-2026-44727)

Summary

Cross-site scripting in jupyter-server (CVE-2026-44727). Risk of unauthorized operations or information disclosure. Exploitable via nbconvert.HTMLExporter. Mitigation: upgrade to 2.20.0 or later.

Original description

The description as published by the source.

The nbconvert HTTP handlers in jupyter_server render user-authored notebook HTML under the Jupyter origin without a sandbox directive in their Content-Security-Policy.

Combined with nbconvert.HTMLExporter's default non-sanitizing behavior, a notebook carrying an HTML payload in a display_data output triggers stored XSS with cookie access, full /api/* authority, and kernel RCE.

Impact

An authenticated victim who navigates to /nbconvert/html/ containing attacker-authored output can have their token exfiltrated to another domain because it is executed in the Jupyter origin.

Patches

Fixed in v2.20.0, commit 6cbee8d

Workarounds

For deployments where editing the installed jupyter_server is impractical (containerized builds, read-only images), adding this to jupyter_server_config.py has the same effect as the patch above without touching source files:

import jupyter_server.nbconvert.handlers as _nb

def _csp(self):
    return super(type(self), self).content_security_policy + "; sandbox allow-scripts"

_nb.NbconvertFileHandler.content_security_policy = property(_csp)
_nb.NbconvertPostHandler.content_security_policy = property(_csp)

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-2026-44727 has been found in jupyter-server.
Attackers can target a specific entry point like nbconvert.HTMLExporter over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.4/10.
What to do: upgrade jupyter-server to 2.20.0 or later.
If unsure, ask your IT team or search "jupyter-server CVE-2026-44727" on the vendor's site.

CVE-2026-44727 (jupyter-server) — CWE-79 / CVSS v3 5.4
Attack vector: remote (network-reachable)
Attack surface: nbconvert.HTMLExporter
Patched: 2.20.0 — 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.

❓ What is the problem

Cross-site scripting (XSS) (CWE-79) exists in jupyter-server. Attackers reach the vulnerable code path via nbconvert.HTMLExporter.

📍 Affected scope

Check the vendor advisory for the affected versions of jupyter-server. Attack surface: nbconvert.HTMLExporter.

🔥 Severity

Severity: Medium (CVSS 5.4/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 2.20.0.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 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 patch patch 
    Upgrade jupyter-server to 2.20.0

    ステージング環境で 2.20.0 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。

  3. 3
    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":"2.20.0"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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