{"id":"GHSA-c3mw-737p-c7g2","summary":"Jupyter Server: 5xx request logging leaks token-bearing Referer header values","details":"### Summary\n\nWhen a request returns a 500, `jupyter_server/log.py` logs a small JSON block of request headers. \n\nThe Referer header was copied into it as-is, so a token in the Referer URL ended up in the logs in plain text.\n\n### Impact\n\nAnyone who can read the server logs can pick tokens out of these 500 entries. Tokens end up in the Referer during normal token-based login and launch flows.\n\nAffected: all versions before 2.21.0.\n\n### PoC\n\nAny malformed request that returns a 500 works:\n\n```bash\ncurl -i -X POST \\\n  -H 'Content-Type: application/json' \\\n  -H 'Referer: http://127.0.0.1:8899/tree?token=REFERTOKEN' \\\n  --data '{\"name\":123}' \\\n  'http://127.0.0.1:8899/api/kernels?token=VALIDTOKEN'\n```\n\nThe log shows the token twice, once raw and once redacted:\n\n```\n\"Referer\": \"http://127.0.0.1:8899/tree?token=REFERTOKEN\",\n[E ... ServerApp] 500 POST /api/kernels?token=[secret] (...) referer=http://127.0.0.1:8899/tree?token=[secret]\n```\n\n### Patches\n\nFixed in 2.21.0 by 5251352. Header values are now scrubbed before the block is logged. Upgrade to 2.21.0 or later.\n\n### Workarounds\n\nLimit who can read the server logs. If you can, avoid flows that put the token in the URL.","aliases":["CVE-2026-86049"],"modified":"2026-09-17T20:45:05.014441361Z","published":"2026-09-17T20:28:55Z","database_specific":{"cwe_ids":["CWE-532"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-09-17T20:28:55Z","nvd_published_at":null},"references":[{"type":"WEB","url":"https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2"},{"type":"WEB","url":"https://github.com/jupyter-server/jupyter_server/pull/1681"},{"type":"WEB","url":"https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717"},{"type":"PACKAGE","url":"https://github.com/jupyter-server/jupyter_server"},{"type":"WEB","url":"https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0"}],"affected":[{"package":{"name":"jupyter-server","ecosystem":"PyPI","purl":"pkg:pypi/jupyter-server"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.21.0"}]}],"versions":["0.0.0","0.0.1","0.0.2","0.0.3","0.0.4","0.0.5","0.1.0","0.1.1","0.2.0","0.2.1","0.3.0","1.0.0","1.0.0rc0","1.0.0rc1","1.0.0rc10","1.0.0rc11","1.0.0rc12","1.0.0rc13","1.0.0rc14","1.0.0rc15","1.0.0rc16","1.0.0rc2","1.0.0rc3","1.0.0rc4","1.0.0rc5","1.0.0rc6","1.0.0rc7","1.0.0rc8","1.0.0rc9","1.0.1","1.0.10","1.0.11","1.0.2","1.0.3","1.0.4","1.0.5","1.0.6","1.0.7","1.0.8","1.0.9","1.1.0","1.1.1","1.1.2","1.1.3","1.1.4","1.10.0","1.10.1","1.10.2","1.11.0","1.11.1","1.11.2","1.12.0","1.12.1","1.13.0","1.13.1","1.13.2","1.13.3","1.13.4","1.13.5","1.15.0","1.15.1","1.15.2","1.15.3","1.15.4","1.15.5","1.15.6","1.16.0","1.17.0","1.17.1","1.18.0","1.18.1","1.19.0","1.19.1","1.2.0","1.2.1","1.2.2","1.2.3","1.21.0","1.23.0","1.23.1","1.23.2","1.23.3","1.23.4","1.23.5","1.23.6","1.24.0","1.3.0","1.4.0","1.4.1","1.5.0","1.5.1","1.6.0","1.6.1","1.6.2","1.6.3","1.6.4","1.7.0","1.7.0a1","1.7.0a2","1.8.0","1.9.0","2.0.0","2.0.0a0","2.0.0a1","2.0.0a2","2.0.0b0","2.0.0b1","2.0.0rc0","2.0.0rc1","2.0.0rc2","2.0.0rc3","2.0.0rc4","2.0.0rc5","2.0.0rc6","2.0.0rc7","2.0.0rc8","2.0.1","2.0.2","2.0.3","2.0.4","2.0.5","2.0.6","2.0.7","2.1.0","2.10.0","2.10.1","2.11.0","2.11.1","2.11.2","2.12.0","2.12.1","2.12.2","2.12.3","2.12.4","2.12.5","2.13.0","2.14.0","2.14.1","2.14.2","2.15.0","2.16.0","2.17.0","2.18.0","2.18.1","2.18.2","2.19.0","2.2.0","2.2.1","2.20.0","2.3.0","2.4.0","2.5.0","2.6.0","2.7.0","2.7.1","2.7.2","2.7.3","2.8.0","2.9.0","2.9.1"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-c3mw-737p-c7g2/GHSA-c3mw-737p-c7g2.json","last_known_affected_version_range":"\u003c= 2.20.0"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H"}]}