23 Oct 2026 15:48:27 UTC
Jupyter Server: 5xx request logging leaks token-bearing Referer header values
cve-program · CVE-2026-86049 · Published
CVE-2026-86049
Jupyter Server: 5xx request logging leaks token-bearing Referer header values
CVSS 3.1 7.1 HIGHCheck source for fixed versionsKEV status unknown
cve-program · CVE-2026-86049
PublishedJupyter 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.
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