Answer in brief
CVE-2026-86049 records a High severity (CVSS 7.1) vulnerability in Jupyter Server: 5xx request logging leaks token-bearing Referer header values. The current sources do not mark it as known exploited. The current feed maps jupyter-server/jupyter_server (generic), jupyter_server (pip), jupyter-server (pypi). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.1. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps jupyter-server/jupyter_server (generic), jupyter_server (pip), jupyter-server (pypi). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| jupyter-server/jupyter_servergeneric | < 2.21.0 | Not reported |
| jupyter_serverpip | <=2.20.0 | 2.21.0 |
| jupyter-serverpypi | >=0 <2.21.0 | 2.21.0 |
Published upstream
Sep 17, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 17, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Sep 17, 2026
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.
Quoted source text, attributed separately from HOL analysis.