Marimo RCE (CVE-2026-39987) exploited for 8-second pivot to SSH bastion

Affected Systems

All versions of Marimo notebook application. CVE-2026-39987 is a pre-authenticated remote code execution vulnerability (CVSS 9.3) actively exploited within hours of public disclosure.

Exploitation Status

Active exploitation confirmed. Skilled human attacker achieved full compromise in 8 seconds, pivoting from Marimo RCE to SSH bastion via AWS Secrets Manager credential theft. Attack observed over 9-hour session with 850+ interactive commands.

Business Impact

Pre-authentication RCE allows immediate shell access without credentials. Attackers can rapidly pivot to cloud infrastructure (AWS Secrets Manager) and internal SSH bastions. Human operators demonstrated machine-speed exploitation, bypassing honeypot traps that caught AI agents. Organizations running Marimo in cloud environments with IAM credentials or secrets access face immediate risk of lateral movement and data exfiltration.

Urgency

🔴 Immediate

Recommended Actions

• Immediately patch or isolate all Marimo notebook instances; no version is safe from CVE-2026-39987
• Audit AWS CloudTrail logs for unauthorized Secrets Manager API calls (GetSecretValue) from Marimo instance roles between disclosure date and present
• Review SSH bastion authentication logs for connections using keys retrieved from Secrets Manager; rotate all SSH keys stored in AWS Secrets Manager accessible to Marimo instances
• Restrict IAM roles attached to Marimo instances to least-privilege; remove Secrets Manager read permissions if not operationally required
• Monitor for WebSocket connections to /terminal/ws endpoint and outbound SSH traffic from application servers; block or alert on unexpected SSH client activity from web application hosts