Jupyter Server: 5xx request logging leaks token-bearing Referer header values

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-86049
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-17 21:17:50 UTC
Updated2026-09-24 21:19:05 UTC
DescriptionJupyter 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.

Risk And Classification

Primary CVSS: v3.1 7.1 HIGH from [email protected]

CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H

EPSS: 0.004160000 probability, percentile 0.331270000 (date 2026-09-24)

Problem Types: CWE-532 | CWE-532 CWE-532: Insertion of Sensitive Information into Log File

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.1HIGHCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H
3.1CNADECLARED7.1HIGHCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Jupyter-server Jupyter Server affected < 2.21.0 Not specified

References

ReferenceSourceLinkTags
github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0 [email protected] github.com
github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-7... [email protected] github.com
github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911... [email protected] github.com
github.com/jupyter-server/jupyter_server/pull/1681 [email protected] github.com
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