CVE-2026-86049
Published:September 17, 2026
Updated:September 22, 2026
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.
Affected Packages
jupyter_server (CONDA):
Affected version(s) >=0.0.2 <2.21.0Fix Suggestion:
Update to version 2.21.0https://github.com/jupyter-server/jupyter_server.git (GITHUB):
Affected version(s) >=v2.12.0 <v2.21.0Fix Suggestion:
Update to version v2.21.0jupyter_server (PYTHON):
Affected version(s) >=0.0.0 <2.21.0Fix Suggestion:
Update to version 2.21.0Related Resources (5)
Do you need more information?
Contact UsCVSS v4
Base Score:
7.5
Attack Vector
NETWORK
Attack Complexity
HIGH
Attack Requirements
NONE
Privileges Required
LOW
User Interaction
PASSIVE
Vulnerable System Confidentiality
HIGH
Vulnerable System Integrity
HIGH
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
7.1
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
LOW
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Weakness Type (CWE)
Insertion of Sensitive Information into Log File
EPSS
Base Score:
0.24