Jupyter Server is the backend for Jupyter web applications. Prior to version 2.21.0, the 5xx request logging path in jupyter_server/log.py copies the Referer header into a JSON header block without applying the token scrubbing used for the request URI. A request that returns HTTP 500 while the Referer contains a token-bearing URL can therefore write that token to server logs in plaintext. An attacker who can read those logs can recover the token and use the affected user's Jupyter Server permissions. This issue is fixed in version 2.21.0.
History

Wed, 23 Sep 2026 00:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-117
References
Metrics threat_severity

None

threat_severity

Moderate


Fri, 18 Sep 2026 21:30:00 +0000

Type Values Removed Values Added
First Time appeared Jupyter
Jupyter jupyter Server
Vendors & Products Jupyter
Jupyter jupyter Server
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Thu, 17 Sep 2026 20:45:00 +0000

Type Values Removed Values Added
Description Jupyter Server is the backend for Jupyter web applications. Prior to version 2.21.0, the 5xx request logging path in jupyter_server/log.py copies the Referer header into a JSON header block without applying the token scrubbing used for the request URI. A request that returns HTTP 500 while the Referer contains a token-bearing URL can therefore write that token to server logs in plaintext. An attacker who can read those logs can recover the token and use the affected user's Jupyter Server permissions. This issue is fixed in version 2.21.0.
Title Jupyter Server: 5xx request logging leaks token-bearing Referer header values
Weaknesses CWE-532
References
Metrics cvssV3_1

{'score': 7.1, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published: 2026-09-17T20:28:52.154Z

Updated: 2026-09-18T18:32:48.654Z

Reserved: 2026-09-04T19:29:21.058Z

Link: CVE-2026-86049

cve-icon Vulnrichment

Updated: 2026-09-18T17:24:13.674Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-09-17T21:17:50.213

Modified: 2026-09-24T21:19:05.340

Link: CVE-2026-86049

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-09-17T20:28:52Z

Links: CVE-2026-86049 - Bugzilla