CVE-2026-86049

Name	CVE-2026-86049
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.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
jupyter-server (PTS)	bookworm	1.23.3-1	vulnerable
	trixie	2.15.0-1	vulnerable
	forky, sid	2.20.0-3	vulnerable

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
jupyter-server	source	(unstable)	(unfixed)

Notes

https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2
https://github.com/jupyter-server/jupyter_server/pull/1681
Fixed by: https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717 (v2.21.0)