CVE-2026-86049
Jupyter Server: 5xx request logging leaks token-bearing Referer header values
Description
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.
INFO
Published Date :
Sept. 17, 2026, 9:17 p.m.
Last Modified :
Sept. 17, 2026, 9:17 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | [email protected] |
Solution
- Update Jupyter Server to 2.21.0 or later.
- Scrub Referer header for tokens before logging.
- Review server logs for exposed tokens.
- Invalidate compromised tokens.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-86049.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-86049 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-86049
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-86049 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-86049 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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New CVE Received by [email protected]
Sep. 17, 2026
Action Type Old Value New Value Added Description 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. Added CVSS V3.1 AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H Added CWE CWE-532 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/86xxx/CVE-2026-86049.json">CVE-2026-86049</a> Added Reference https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717 Added Reference https://github.com/jupyter-server/jupyter_server/pull/1681 Added Reference https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0 Added Reference https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2