CVE-2026-44727: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in jupyter-server jupyter_server
A critical cross-site scripting (XSS) vulnerability exists in jupyter_server prior to version 2.20. The nbconvert HTTP handlers render user-authored notebook HTML without a sandbox directive in the Content-Security-Policy, combined with default non-sanitizing behavior of nbconvert.HTMLExporter. This allows stored XSS that can lead to cookie access, full API authority, and kernel remote code execution. The vulnerability is fixed in version 2.20.
AI Analysis
Technical Summary
CVE-2026-44727 is a stored cross-site scripting vulnerability in jupyter_server's nbconvert HTTP handlers before version 2.20. The handlers render user-authored notebook HTML under the Jupyter origin without a sandbox directive in the Content-Security-Policy header. Because nbconvert.HTMLExporter does not sanitize HTML output by default, a malicious notebook containing crafted HTML payloads in display_data outputs can trigger stored XSS. Successful exploitation can result in cookie theft, full access to the /api/* endpoints, and remote code execution on the kernel. The issue is resolved in jupyter_server version 2.20.
Potential Impact
Exploitation of this vulnerability allows an attacker to execute arbitrary scripts in the context of the Jupyter Server web application. This can lead to theft of authentication cookies, unauthorized full access to the Jupyter API endpoints, and remote code execution on the kernel, potentially compromising the entire server environment.
Mitigation Recommendations
This vulnerability is fixed in jupyter_server version 2.20. Users should upgrade to version 2.20 or later to remediate this issue. No other official remediation or temporary fixes are indicated. Patch status is not explicitly confirmed in the vendor advisory, but the fix is stated to be in version 2.20.
CVE-2026-44727: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in jupyter-server jupyter_server
Description
A critical cross-site scripting (XSS) vulnerability exists in jupyter_server prior to version 2.20. The nbconvert HTTP handlers render user-authored notebook HTML without a sandbox directive in the Content-Security-Policy, combined with default non-sanitizing behavior of nbconvert.HTMLExporter. This allows stored XSS that can lead to cookie access, full API authority, and kernel remote code execution. The vulnerability is fixed in version 2.20.
CVSS v4.0
Score 9.3critical
Affected software
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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-44727 is a stored cross-site scripting vulnerability in jupyter_server's nbconvert HTTP handlers before version 2.20. The handlers render user-authored notebook HTML under the Jupyter origin without a sandbox directive in the Content-Security-Policy header. Because nbconvert.HTMLExporter does not sanitize HTML output by default, a malicious notebook containing crafted HTML payloads in display_data outputs can trigger stored XSS. Successful exploitation can result in cookie theft, full access to the /api/* endpoints, and remote code execution on the kernel. The issue is resolved in jupyter_server version 2.20.
Potential Impact
Exploitation of this vulnerability allows an attacker to execute arbitrary scripts in the context of the Jupyter Server web application. This can lead to theft of authentication cookies, unauthorized full access to the Jupyter API endpoints, and remote code execution on the kernel, potentially compromising the entire server environment.
Mitigation Recommendations
This vulnerability is fixed in jupyter_server version 2.20. Users should upgrade to version 2.20 or later to remediate this issue. No other official remediation or temporary fixes are indicated. Patch status is not explicitly confirmed in the vendor advisory, but the fix is stated to be in version 2.20.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-05-07T18:04:17.309Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a39a0f5eed863c81e6b01d7
Added to database: 06/22/2026, 20:54:13 UTC
Last enriched: 06/22/2026, 21:09:16 UTC
Last updated: 06/22/2026, 22:15:59 UTC
Views: 4
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