Jupyter Server: 5xx request logging leaks token-bearing Referer header values
Priority LOW 33CWE-532Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- Required
- Attack complexity
- High
- Impact type
- Information disclosure
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Partial Red Hat: 2 fixed, 2 without a fix
Attack profile from CVSS 3.1 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-532.
Summary
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.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00416 36th percentileScored 2026-11-07
Fix Partial jupyter_server (jupyter-server): 2.21.0jupyter_server (PyPI): 2.21.0Red Hat: 2 advisoriesRed Hat: 2 fixed, 2 without a fix
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| jupyterlab | jupyter_server | before 2.21.0 | 2.21.0 | Patch available | CNA |
| — | jupyter_server (PyPI) | before 2.21.0 | 2.21.0 | Patch available | GHSA-c3mw-737p-c7g2 |
- jupyter_server Vendorjupyterlab Affected before 2.21.0 Fixed in 2.21.0 Patch available CNA
- jupyter_server (PyPI) Vendor— Affected before 2.21.0 Fixed in 2.21.0 Patch available GHSA-c3mw-737p-c7g2
CPE names Threatist (inferred) · 1
Inferred from how NVD named this product before; not given by a source.
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:jupyter:jupyter_server:*:*:*:*:*:*:*:* | — | — | jupyterlab |
- cpe:2.3:a:jupyter:jupyter_server:*:*:*:*:*:*:*:* Versions — — ·jupyterlab
Remediation
- Fix · CNA jupyter_server (jupyter-server) Fixed in 2.21.0
- Fix · GHSA-c3mw-737p-c7g2 jupyter_server (PyPI) Fixed in 2.21.0 Advisory →
Red Hat 2 advisories
- RHSA-2026:87410 Released 2026-10-21 · Red Hat rating CriticalRHOAI 2.25.12 - Red Hat OpenShift AI
- Red Hat OpenShift AI 2.25 registry.redhat.io/rhoai/odh-built-in-detector-rhel9, registry.redhat.io/rhoai/odh-caikit-nlp-rhel9, registry.redhat.io/rhoai/odh-codeflare-operator-rhel9 +47
- RHSA-2026:84734 Released 2026-10-19 · Red Hat rating CriticalRHOAI 3.4.5 - Red Hat OpenShift AI
- Red Hat OpenShift AI 3.4 registry.redhat.io/rhoai/odh-ai-gateway-payload-processing-rhel9, registry.redhat.io/rhoai/odh-automl-rhel9, registry.redhat.io/rhoai/odh-autorag-rhel9 +47
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Migration Toolkit for Applications 8 | Affected | No fix planned: Out of support scope |
| Red Hat OpenShift AI (RHOAI) | Affected | No fix yet |
| Red Hat OpenShift AI 2.25 | Fixed | RHSA-2026:87410 |
| Red Hat OpenShift AI 3.4 | Fixed | RHSA-2026:84734 |
Not affected: 3 products
- Red Hat OpenShift AI (RHOAI)
- Red Hat OpenShift AI 2.25
- Red Hat OpenShift AI 3.4
Timeline
- 2026-10-02 Threatist record created from CVE-2026-86049
- 2026-10-03 Alias added: GHSA-c3mw-737p-c7g2
- 2026-10-16 Affected versions changed · Red Hat
- 2026-10-20 Fix available: RHSA-2026:84734 · Red Hat
- 2026-10-20 Fix available: Red Hat OpenShift AI 3.4 · Red Hat
- 2026-10-22 Fix available: RHSA-2026:87410 · Red Hat
- 2026-10-23 Fix available: Red Hat OpenShift AI 2.25 · Red Hat
References
Other 5
- https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2
- https://github.com/jupyter-server/jupyter_server/pull/1681
- https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717
- https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0
- https://github.com/jupyter-server/jupyter_server
More jupyterlab vulnerabilities
- TI-2026-32161 Jupyter Enterprise Gateway Has Kubernetes Manifest Injection via Jinja2 Template Rendering CVSS 4.0CRITICAL 10.0
- TI-2026-32160 Jupyter Enterprise Gateway: Jinja2 Template Server Side Template Injection results in Remote Code Execution CVSS 4.0CRITICAL 10.0
- TI-2026-32159 Jupyter Enterprise Gateway: ContainerProcessProxy._enforce_prohibited_ids can be Bypassed CVSS 3.1CRITICAL 9.8
- TI-2024-26623 Remote Code Execution (RCE) vulnerability in jupyterlab extension template `update-integration-tests` GitHub Action CVSS 3.1CRITICAL 10.0
- TI-2026-78983 Path traversal in nbconvert lets crafted notebooks write files CVSS 4.0HIGH 8.8
- TI-2026-39372 JupyterLab Git: Stored XSS leading to RCE CVSS 4.0CRITICAL 9.3
Sources
- CVE-2026-86049 · CVE Program
- CVE-2026-86049 · NVD
- FIRST EPSS
- GHSA-c3mw-737p-c7g2 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-86049 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences