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.

No CVSS v4.0

Attack Vector Network

Attack Complexity High

Privileges Required Low

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction Required

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
jupyter-server jupyter_server affected
Version Status Constraints
< 2.21.0 affected —

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Project Subscriptions

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-c3mw-737p-c7g2 Jupyter Server: 5xx request logging leaks token-bearing Referer header values
Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717 cve-icon
https://github.com/jupyter-server/jupyter_server/pull/1681 cve-icon
https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0 cve-icon
https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2 cve-icon
History

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'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

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

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

Link: CVE-2026-86049

cve-icon Vulnrichment

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cve-icon NVD

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cve-icon Redhat

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cve-icon OpenCVE Enrichment

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Weaknesses