Jupyter Server up to 2.20.x Request Logging jupyter_server/log.py Referer log file

Summaryinfo

A vulnerability was found in Jupyter Server up to 2.20.x. It has been classified as problematic. This vulnerability affects unknown code of the file jupyter_server/log.py of the component Request Logging. The manipulation of the argument Referer leads to log file. This vulnerability is traded as CVE-2026-86049. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in Jupyter Server up to 2.20.x. It has been rated as problematic. This issue affects an unknown code block of the file jupyter_server/log.py of the component Request Logging. The manipulation of the argument Referer with an unknown input leads to a log file vulnerability. Using CWE to declare the problem leads to CWE-532. Information written to log files can be of a sensitive nature and give valuable guidance to an attacker or expose sensitive user information. Impacted is integrity. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-86049 since 09/04/2026. The exploitation is known to be easy. The attack may be initiated remotely. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1592 for this issue.

Upgrading to version 2.21.0 eliminates this vulnerability.

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Productinfo

Name

• Jupyter Server

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6
• 2.7
• 2.8
• 2.9
• 2.10
• 2.11
• 2.12
• 2.13
• 2.14
• 2.15
• 2.16
• 2.17
• 2.18
• 2.19
• 2.20

CPE 2.3info

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CPE 2.2info

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