CVE-2026-86049: Jupyter — HIGH

Q: Is CVE-2026-86049 actively exploited?

No confirmed active exploitation of CVE-2026-86049 has been reported, but organizations should still patch proactively.

Q: How to fix CVE-2026-86049?

Update to patched version: Jupyter 2.21.0.

Q: What is the CVSS score for CVE-2026-86049?

CVE-2026-86049 has a CVSS v3.1 base score of 7.1 (HIGH). The EPSS exploitation probability is 0.24%.

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...

Full CISO analysis pending enrichment.

What systems are affected?

Package	Ecosystem	Vulnerable Range	Patched
Jupyter	pip	<= 2.20.0	`2.21.0`
13.3K OpenSSF 5.7 1.9K dependents Pushed 9d ago 57% patched ~35d to patch Full package profile →

Do you use Jupyter? You're affected.

How severe is it?

CVSS 3.1

7.1 / 10

EPSS

0.2%

chance of exploitation in 30 days

Higher than 15% of all CVEs

Source: EPSS v3 — FIRST.org

Exploitation Status

No known exploitation

Sophistication

N/A

What is the attack surface?

AV Network

AC High

PR Low

UI Required

S Unchanged

C High

I High

A High

What should I do?

Patch available

Update Jupyter to version 2.21.0

Which compliance frameworks are affected?

Compliance analysis pending. Sign in for full compliance mapping when available.

Frequently Asked Questions

What is CVE-2026-86049?

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.

Is CVE-2026-86049 actively exploited?

No confirmed active exploitation of CVE-2026-86049 has been reported, but organizations should still patch proactively.

How to fix CVE-2026-86049?

Update to patched version: Jupyter 2.21.0.

What is the CVSS score for CVE-2026-86049?

CVE-2026-86049 has a CVSS v3.1 base score of 7.1 (HIGH). The EPSS exploitation probability is 0.24%.

What are the technical details?

Original Advisory

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.

Weaknesses (CWE)

CWE-532 Insertion of Sensitive Information into Log File Primary CWE-532 Insertion of Sensitive Information into Log File Primary CWE-532 Insertion of Sensitive Information into Log File

CWE-532 — Insertion of Sensitive Information into Log File: The product writes sensitive information to a log file.

[Architecture and Design, Implementation] Consider seriously the sensitivity of the information written into log files. Do not write secrets into the log files.
[Distribution] Remove debug log files before deploying the application into production.

Source: MITRE CWE corpus.