CVE-2026-86049
High
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.
SeverityHigh
CVSS7.1
Exploit probability—
ProductJupyter-server
PublishedSep 17, 2026
First seenSep 17, 2026
Weakness typeCWE-532CWE-532
How to fix
Update
- jupyter-server2.21.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| jupyter-serverPyPI | v < 2.21.0 | 2.21.0 |
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