Security readout for executives and security teams
Plain-English summary
A malicious notebook can hide dangerous JupyterLab actions behind a normal-looking HTML button. If a user clicks it, JupyterLab may run commands, potentially including code execution, without the user knowingly submitting code. The issue is fixed in JupyterLab 4.5.7.
Executive priority
Prioritize remediation for research, data science, AI, and education environments where users open shared notebooks. The business risk is high because one click in trusted-looking notebook content can lead to code execution in the user’s Jupyter context.
Technical view
Before JupyterLab 4.5.7, the HTML sanitizer allowed command-linker attributes on button elements, while CommandLinker handled body click events and executed named commands without validating trusted UI origin. A saved HTML cell output could therefore trigger arbitrary JupyterLab commands after one user click.
Likely exposure
Exposure is likely where JupyterLab versions before 4.5.7 or Jupyter Notebook versions 7.0.0 through before 7.5.6 are used, especially with notebooks from external repositories, vendors, students, partners, or other untrusted sources.
Exploitation context
The source bundle says exploitation requires user interaction: a click on deceptive saved HTML output. It reports KEV status as false, and no provided source states active exploitation in the wild.
Researcher notes
The key trust-boundary failure is sanitizer allowlisting of command-linker attributes combined with global click handling that does not verify trusted UI provenance. Evidence in the bundle supports arbitrary command execution after a click, but not active exploitation.
Mitigation direction
- Upgrade JupyterLab to 4.5.7 or later.
- For Jupyter Notebook 7 deployments, check vendor guidance for fixed notebook packages.
- Treat notebooks from untrusted sources as unsafe until reviewed or opened in isolation.
- Restrict sharing and execution workflows for externally supplied notebooks.
- Monitor Jupyter and distribution vendor advisories for package-specific updates.
Validation and detection
- Inventory deployed JupyterLab and Jupyter Notebook versions.
- Confirm no JupyterLab instance remains below 4.5.7.
- Confirm Notebook 7 instances are not in the affected version range.
- Review notebook intake processes for untrusted saved HTML outputs.
- Check vendor security advisories for downstream package status.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-79: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-42557 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
2 official scoresWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H2.85.9redhat-SADPCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N——GitHub_MVulnerability scoring details
Base CVSS 4.0 score
8.6HighVector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Base CVSS 3.1 score
8.8HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- ADP timelineredhat-SADP
Made public.
- CVE publishedCVE Program
The CVE record was published.
- ADP timelineredhat-SADP
Reported to Red Hat.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
- 2026-05-13T16:02:57.063Z: Reported to Red Hat.
- 2026-05-13T15:06:14.222Z: Made public.
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/jupyterlab/jupyterlab/security/advisories/GHSA-mqcg-5x36-vfcgCVE reference, GitHub_M · x_refsource_CONFIRM
- https://access.redhat.com/security/cve/CVE-2026-42557CVE reference, redhat-SADP · vdb-entry, x_refsource_REDHAT
- RHBZ#2477086CVE reference, redhat-SADP · issue-tracking, x_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42557.jsonCVE reference, redhat-SADP · x_sadp-csaf-vex
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.