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GHSA-c3mw-737p-c7g2
jupyter-serverSummary
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:
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.
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The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker needs basic access or low-level privileges. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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