GHSA-c3mw-737p-c7g2

Source

https://github.com/advisories/GHSA-c3mw-737p-c7g2

Import Source

https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-c3mw-737p-c7g2/GHSA-c3mw-737p-c7g2.json

JSON Data

https://api.osv.dev/v1/vulns/GHSA-c3mw-737p-c7g2

Aliases

CVE-2026-86049

Published

2026-09-17T20:28:55Z

Modified

2026-09-17T20:45:05Z

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.

Database specific

{
    "cwe_ids": [
        "CWE-532"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-17T20:28:55Z",
    "nvd_published_at": null,
    "severity": "HIGH"
}

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

last_known_affected_version_range

"<= 2.20.0"

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-c3mw-737p-c7g2/GHSA-c3mw-737p-c7g2.json"