PT-2026-105810 · Pypi · Jupyter Server
Published
2026-10-01
·
Updated
2026-10-01
CVSS v3.1
7.1
High
| Vector | AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H |
Summary
When a request returns a 500,
jupyter server/log.py logs a small JSON block of request headers.The Referer header was copied into it as-is, so a token in the Referer URL ended up in the logs in plain text.
Impact
Anyone 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.
Affected: all versions before 2.21.0.
PoC
Any malformed request that returns a 500 works:
bash
curl -i -X POST
-H 'Content-Type: application/json'
-H 'Referer: http://127.0.0.1:8899/tree?token=REFERTOKEN'
--data '{"name":123}'
'http://127.0.0.1:8899/api/kernels?token=VALIDTOKEN'The log shows the token twice, once raw and once redacted:
"Referer": "http://127.0.0.1:8899/tree?token=REFERTOKEN",
[E ... ServerApp] 500 POST /api/kernels?token=[secret] (...) referer=http://127.0.0.1:8899/tree?token=[secret]Patches
Fixed in 2.21.0 by 5251352. Header values are now scrubbed before the block is logged. Upgrade to 2.21.0 or later.
Workarounds
Limit who can read the server logs. If you can, avoid flows that put the token in the URL.
Fix
Found an issue in the description? Have something to add? Feel free to write us 👾
Related Identifiers
Affected Products
Jupyter Server