A critical security vulnerability in Marimo, an open-source Python notebook for data science and analysis, has been actively exploited within just 10 hours of public disclosure, highlighting the growing speed of weaponization in the modern threat landscape.
Overview
CVE-2026-39987 is a Remote Code Execution (RCE) vulnerability affecting Marimo versions prior to 0.8.12. The flaw exists in the notebook’s cell execution engine, allowing an attacker to craft a malicious notebook file that executes arbitrary code on the host system when opened.
Technical Details
The vulnerability stems from:
- Insufficient sandboxing of Python cell execution
- Lack of input validation on notebook import functionality
- Deserialization of untrusted data from shared notebook URLs
CVSS Score: 9.8 Critical (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)
Impact Assessment
Data science teams and research environments using shared Marimo notebooks are at highest risk. Exploitation can lead to complete host compromise, data exfiltration, and lateral movement within research networks.
Affected Versions
- Marimo < 0.8.12 — Vulnerable
- Marimo >= 0.8.12 — Patched
Recommended Mitigations
- Update Marimo immediately:
pip install --upgrade marimo - Never open notebook files from untrusted sources
- Run Marimo in isolated Docker containers
- Review shared notebook URLs for malicious content
Written by Tarang Parmar (CEH) — TheCyberSecurity.Network. Read time: 4 min.