PYSEC-2026-4054

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Import Source
https://github.com/pypa/advisory-database/blob/main/vulns/jupyter-server/PYSEC-2026-4054.yaml
JSON Data
https://api.osv.dev/v1/vulns/PYSEC-2026-4054
Aliases
Published
2026-10-01T16:38:33Z
Modified
2026-10-01T17:45:05Z
Severity
  • 7.1 (High) CVSS_V3 - CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H CVSS Calculator
Summary
Jupyter Server: 5xx request logging leaks token-bearing Referer header values
Details

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:

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.

References

Affected packages

PyPI / jupyter-server

Package

Name
jupyter-server
View open source insights on deps.dev
Purl
pkg:pypi/jupyter-server

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected
Fixed
2.21.0

Affected versions

0.*
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.*
1.0.0rc0
1.0.0rc1
1.0.0rc2
1.0.0rc3
1.0.0rc4
1.0.0rc5
1.0.0rc6
1.0.0rc7
1.0.0rc8
1.0.0rc9
1.0.0rc10
1.0.0rc11
1.0.0rc12
1.0.0rc13
1.0.0rc14
1.0.0rc15
1.0.0rc16
1.0.0
1.0.1
1.0.2
1.0.3
1.0.4
1.0.5
1.0.6
1.0.7
1.0.8
1.0.9
1.0.10
1.0.11
1.1.0
1.1.1
1.1.2
1.1.3
1.1.4
1.2.0
1.2.1
1.2.2
1.2.3
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
1.7.0a1
1.7.0a2
1.7.0
1.8.0
1.9.0
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
1.21.0
1.23.0
1.23.1
1.23.2
1.23.3
1.23.4
1.23.5
1.23.6
1.24.0
2.*
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
2.0.0
2.0.1
2.0.2
2.0.3
2.0.4
2.0.5
2.0.6
2.0.7
2.1.0
2.2.0
2.2.1
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
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
2.20.0

Database specific

source 
"https://github.com/pypa/advisory-database/blob/main/vulns/jupyter-server/PYSEC-2026-4054.yaml"