CVE-2026-39987: Marimo Remote Code Execution Vulnerability

What it is

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.

Exploitation evidence

First exploit evidence seen: 2026-04-12 (earliest date across the sources below).

Exploited in the wild

• CISA KEV: listed since 2026-04-23. Source

Public exploit code

Exploit-DB

• EDB-52673: Marimo 0.20.4 - RCE (2026-09-02)

GitHub proof-of-concept repositories

29 public repositories from 29 accounts, first seen 2026-04-12. Most starred: Th3Purge/CVE-2026-39987 (9 stars), view repository.

Verify before running: public PoCs can be malicious. Read the code and only run it in an isolated lab. A PoC means exploit code is public, not that this CVE is exploited in the wild.

Sources: CISA KEV · Exploit-DB (OffSec) · nomi-sec/PoC-in-GitHub.

How to fix it

CISA required action

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. (source: CISA KEV)

Fixed versions

• coreweave marimo: upgrade to 0.23.0 or later

Derived from the NVD CPE configuration (versionEndExcluding / versionEndIncluding). Always confirm with the vendor advisory.

Vendor advisories and patches

• https://github.com/marimo-team/marimo/security/advisories/GHSA-2679-6mx9-h9xc (CISA KEV notes)
• https://github.com/marimo-team/marimo/commit/c24d4806398f30be6b12acd6c60d1d7c68cfd12a (Patch)
• https://github.com/marimo-team/marimo/pull/9098 (Issue Tracking, Patch)

MITRE ATT&CK mitigations for this chain

• M1048 Application Isolation and Sandboxing (for T1190) : Application isolation will limit what other processes and system features the exploited target can access.
• M1037 Filter Network Traffic (for T1190) : Restrict outbound network traffic from public-facing servers to prevent unauthorized connections from initiating communications with attacker-controlled infrastructure. While this may not prevent the initial exploitation, it limits the attacker's ability to verify and control the compromised server post-exploit, reduci
• M1030 Network Segmentation (for T1190) : Segment externally facing servers and services from the rest of the network with a DMZ or on separate hosting infrastructure.
• M1016 Vulnerability Scanning (for T1190) : Regularly scan externally facing systems for vulnerabilities and establish procedures to rapidly patch systems when critical vulnerabilities are discovered through scanning and through public disclosure.
• M1026 Privileged Account Management (for T1190, T1078) : Use least privilege for service accounts will limit what permissions the exploited process gets on the rest of the system.
• M1050 Exploit Protection (for T1190) : Web Application Firewalls may be used to limit exposure of applications to prevent exploit traffic from reaching the application.
• M1035 Limit Access to Resource Over Network (for T1190) : Ensure that all publicly exposed services are actually intended to be so, and restrict access to any that should only be available internally.
• M1051 Update Software (for T1190) : Update software regularly by employing patch management for externally exposed applications.
• M1027 Password Policies (for T1078) : Applications and appliances that utilize default username and password should be changed immediately after the installation, and before deployment to a production environment. When possible, applications that use SSH keys should be updated periodically and properly secured. Policies should minimize (if not eliminate)
• M1018 User Account Management (for T1078) : Regularly audit user accounts for activity and deactivate or remove any that are no longer needed.

Detection Generic guidance

• Initial Access: Alert on unusual requests to the affected service (odd paths, oversized payloads, exploit strings) in WAF, reverse-proxy and application logs.
• Persistence: Look for new files in web roots, new scheduled tasks/services, and new accounts created after the exposure window.
• Privilege Escalation: Alert on processes gaining SYSTEM/root unexpectedly, and on exploitation crashes of privileged services.

Response checklist Generic guidance

1. Inventory: find every instance of the affected product and version (include internet-facing and forgotten ones).
2. Patch or mitigate per the vendor advisory; if you cannot patch, remove internet exposure or apply the vendor workaround.
3. Assume compromise if the system was exposed before patching: hunt for the indicators in the advisory and review logs back to the disclosure date.
4. Rotate credentials and secrets stored on or used by the affected system if compromise cannot be ruled out.