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Vulnerability record · CVE-2026-86049 · published 17 September 2026

CVE-2026-86049: Sensitive information in log file vulnerability

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.

7.1 CVSS 3.1 High EPSS 0.42% · top 66.7% CWE-532 · Sensitive information in log file Awaiting Analysis
7.1CVSS 3.1 base score
0.42%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
4References
24 Sep 2026Last modified by NVD

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.

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

References

LinkTags
https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717
https://github.com/jupyter-server/jupyter_server/pull/1681
https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0
https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2

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Source: NIST National Vulnerability Database (record CVE-2026-86049), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.