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VulnerabilityPublished

CVE-2026-86049: jupyter_server · Sensitive Data in Logs

Affects jupyter_serverSource CVE Database V5

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Not known to be exploited · CVSS 7.1 High : upgrade to 2.21.0 soon.

Data as of 1 Nov 2026, 11:03 UTC

CVSS 3.1 base score
7.1High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.4% chance of exploitation in 30 days – higher than 35% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 2.21.0
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 17 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 1 Nov 2026.

What to do

Upgrade jupyter_server and jupyter-server to 2.21.0.

Affected software

ProductAffectedFixed in
jupyter-serverjupyter_serverAffected
  • <2.21.0
Fixed in
  • 2.21.0
PyPIjupyter-serverpkg:pypi/jupyter-serverOther threatsAffected
  • <2.21.0
Fixed in
  • 2.21.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade Jupyter Server to version 2.21.0 or later, where this vulnerability is fixed. No other mitigation is specified or required as the fix addresses the root cause by properly scrubbing tokens from the Referer header before logging.

Description

Jupyter Server versions prior to 2.21.0 contain a vulnerability where the Referer header is logged without scrubbing sensitive tokens during 5xx error responses. This can lead to sensitive tokens being stored in plaintext in server logs. An attacker with access to these logs could recover tokens and gain the affected user's permissions. The issue is fixed in version 2.21.0.

References

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