CVE-2026-86049
HIGHDescription
Jupyter Server is the backend for Jupyter web applications. Prior to version 2.21.0, the 5xx request logging path in jupyter_server/log.py copies the Referer header into a JSON header block without applying the token scrubbing used for the request URI. A request that returns HTTP 500 while the Referer contains a token-bearing URL can therefore write that token to server logs in plaintext. An attacker who can read those logs can recover the token and use the affected user's Jupyter Server permissions. This issue is fixed in version 2.21.0.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H
Exploit Intelligence
EPSS data unavailable for this CVE.
References
Related Vulnerabilities
Other CWE-532 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2019-1622 | Medium | 5.3 | 79% | - | - |
| CVE-2020-35234 | High | 7.5 | 65% | - | Fix |
| CVE-2023-43261 | High | 7.5 | 60% | - | Fix |
| CVE-2024-20440 | High | 7.5 | 52% | - | - |
| CVE-2018-3609 | High | 8.1 | 21% | - | - |
| CVE-2018-8719 | Medium | 5.3 | 16% | - | - |
Common questions
How do I fix CVE-2026-86049?
No published fix for CVE-2026-86049 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
How severe is CVE-2026-86049?
CVE-2026-86049 has a CVSS v3 base score of 7.1, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-17.