CVE-2026-86049

HIGHPre-NVD 7.17.1—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.1 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.2%, top 85% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Trending — 3 sources updated this week
7.1EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.1Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
7.1
EG Score
7.1(medium)
EG Risk
32(Track)
EG Risk 32/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity71% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
15%
KEV
Not listed

Published

September 17, 2026

Last Modified

September 18, 2026

Advisory Details (4)

Auto-updated Sep 17, 2026
🔬 Proof of concept available. Patch available. Sources: github_release, github, github_pr, github_commit.
github_release Patch Available

v2.21.0

Patch available: jupyter-server/jupyter_server v2.21.0

https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0
github_commit Patch Available

commit 52513529af70 (jupyter-server/jupyter_server)

Patch available: jupyter-server/jupyter_server v2.21.0 (contains commit 52513529af70)

https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717
github_pr Patch Available

Fix referer token leak in server logs when the request causes a 500

Patch available: jupyter-server/jupyter_server v2.21.0 (PR #1681 merged 2026-07-20)

https://github.com/jupyter-server/jupyter_server/pull/1681
github Patch Available🟡 PoC Available

5xx request logging leaks token-bearing Referer header values · Advisory · jupyter-server/jupyter_server · GitHub

Affected: 2.21.0 by

https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2

Vendor Advisories for CVE-2026-86049(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFixed inDependents
jupyter-server0.0.0 ... 2.9.1 (160 versions)2.21.0—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 7× in last 7d / 7× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-19 06:48 UTCEG score recompute
  2. 2026-09-18 19:28 UTCEPSS rescore
  3. 2026-09-18 19:28 UTCEG score recompute
  4. 2026-09-18 18:44 UTCEG score recompute
  5. 2026-09-17 21:20 UTCEG score recompute
  6. 2026-09-17 20:34 UTCEG score recompute
  7. 2026-09-17 20:34 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-86049?
CVE-2026-86049 is a high vulnerability published on September 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…
When was CVE-2026-86049 disclosed?
CVE-2026-86049 was first published in the National Vulnerability Database on September 17, 2026, with the most recent update on September 18, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-86049 actively exploited?
CVE-2026-86049 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 84.8% of all scored CVEs.
What is the CVSS score of CVE-2026-86049?
CVE-2026-86049 has a CVSS v3 base score of 7.1 (NVD).
How do I remediate CVE-2026-86049?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-86049, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-86049

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