CVE Exploit Alert: CVE-2026-39987 | CRITICAL | CVSS 9.3 | Marimo Marimo

CRITICAL

Alert Date: 2026-05-02

Severity Overview

Summary

marimo is a reactive Python notebook. Prior to 0.23.0, Marimo has a Pre-Auth RCE vulnerability. The terminal WebSocket endpoint /terminal/ws lacks authentication validation, allowing an unauthenticated attacker to obtain a full PTY shell and execute arbitrary system commands. Unlike other WebSocket endpoints (e.g., /ws) that correctly call validate_auth() for authentication, the /terminal/ws endpoint only checks the running mode and platform support before accepting connections, completely skipping authentication verification. This vulnerability is fixed in 0.23.0.

What the Attack Looks Like

How it works: A function that should require authentication is reachable without any, granting direct unauthenticated access to sensitive operations or administrative capabilities.

Analyst Takeaway

The attack is launched over the network (remotely exploitable without physical access) and no authentication is required. This vulnerability is already in CISA KEV, which means exploitation has been confirmed in the wild — treat this as active risk, not theoretical exposure. The CVSS score places this in critical territory, so internet-facing systems and high-value assets should be prioritized for immediate remediation or compensating controls. In parallel with patching, defenders should review external exposure, hunt for signs of exploitation, and validate whether compensating controls are in place for vulnerable assets.

Detection Guidance

• CWE-306 — Missing Authentication for Critical Function
  • Unauthenticated access to sensitive endpoints: Search access logs for requests to admin, management, or configuration endpoints that carry no authentication headers or session tokens. These requests should be rare to nonexistent in a properly configured deployment.
  • Source IP analysis: Flag access to management interfaces from external IPs or IPs outside your admin network range. The absence of authentication makes these endpoints especially attractive for opportunistic attackers.
  • Functional impact review: If unauthenticated access is detected, review what actions were taken during those sessions — account creation, configuration changes, file access — to assess the full scope of any compromise.

Recommended Actions

Immediate (0–24 Hours)

• Inventory: Identify all systems running Marimo Marimo. Include production, staging, dev, and cloud environments — untracked instances are the most likely to remain unpatched.
• Validate internet-facing exposure: Determine which of the affected systems are reachable from the public internet. Prioritize these for immediate remediation or compensating controls.
• Apply compensating controls now: For systems that cannot be patched immediately, implement temporary mitigations: restrict access via firewall rules or ACLs, add WAF rules if applicable, disable or isolate the vulnerable component if feasible without breaking critical operations.

Remediation

• Apply the vendor patch: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
• CISA directive deadline: 2026-05-07 — this is the mandatory deadline for US federal civilian agencies under BOD 22-01. All organizations should treat this date as a strong target regardless of federal mandate.
• Verify remediation: After patching, confirm the correct version is installed on all affected hosts. Run a vulnerability scan or use your asset management tooling to verify — do not rely solely on change tickets.

Detection Coverage

• Unauthenticated exploitation monitoring: Because this vulnerability requires no authentication, internet-facing scanning and exploitation attempts may begin within hours of public disclosure. Ensure alerting is in place before the end of the day.
• Threat intelligence feeds: Monitor your TI feeds and vendor advisory channels for published indicators of compromise (IOCs), proof-of-concept exploit releases, or active campaign reporting associated with this CVE — these should trigger an immediate hunt even if no internal alerts have fired.

Vulnerability Details

Additional Notes

https://github.com/marimo-team/marimo/security/advisories/GHSA-2679-6mx9-h9xc ; https://nvd.nist.gov/vuln/detail/CVE-2026-39987