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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

Original advisory

cve-program · CVE-2026-86049

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-86049

Published

jupyter_server

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "jupyter-server",
                    "product": "jupyter_server",
                    "versions": [
                        {
                            "version": "< 2.21.0",
                            "status": "affected"
                        }
                    ]
                }

Original source record · Cite this exact observation · Complete original publisher JSON