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CVE-2026-44727— Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP

Quick assessment

Affected
jupyter-server jupyter_server
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

jupyter-server jupyter_server是jupyter-server的Web服务器。 Jupyter Server 2.20之前版本存在安全漏洞，该漏洞源于nbconvert HTTP handlers在渲染用户编写的笔记本HTML时未设置沙箱指令的Content-Security-Policy，结合nbconvert.HTMLExporter的默认非清理行为，可能导致存储型跨站脚本攻击，获取cookie、完整的/api/*权限及内核远程代码执行。

CVSS 9.3 · Critical EPSS 0.44% · P36

Affected Version Matrix 1

VendorProduct Version RangeStatus
jupyter-server jupyter_server < 2.20 affected
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I. Basic Information for CVE-2026-44727

Vulnerability Information
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Vulnerability Title
Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP
Source: CVE Program / CVE List V5
Vulnerability Description
Jupyter Server is the backend for Jupyter web applications. Prior to 2.20, 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. This vulnerability is fixed in 2.20.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5
Vulnerability Title
Jupyter Server 处理逻辑错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
jupyter-server jupyter_server是jupyter-server的Web服务器。 Jupyter Server 2.20之前版本存在安全漏洞，该漏洞源于nbconvert HTTP handlers在渲染用户编写的笔记本HTML时未设置沙箱指令的Content-Security-Policy，结合nbconvert.HTMLExporter的默认非清理行为，可能导致存储型跨站脚本攻击，获取cookie、完整的/api/*权限及内核远程代码执行。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
jupyter-server jupyter_server < 2.20 -

II. Public POCs for CVE-2026-44727

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III. Intelligence Information for CVE-2026-44727

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Patches & Fixes for CVE-2026-44727 (1)

Vendor Advisories for CVE-2026-44727 (1)

IV. Related Vulnerabilities

Same product: jupyter_server
Same vendor: jupyter-server
Same weakness: CWE-79

V. Comments for CVE-2026-44727

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