CVE-2026-39987: listed in the CISA KEV catalog

CVE-2026-39987 · EPSS 97% · KEV 2026-04-23

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.

Is CVE-2026-39987 exploited?

• Listed in the CISA KEV catalog on 2026-04-23.
• Federal remediation due 2026-05-07.
• Past that date by 100 days.
• EPSS puts exploitation in the next 30 days at 97%.
• Public exploit code: none found in monitored sources.
• Public detection rules exist.

Which products and versions are affected?

No affected package list recorded here yet.

Is there a patch?

No patch identifier recorded here yet.

What PlainSec published about CVE-2026-39987

• Marimo Zero-Day Turns AI Demo Hosting Into Malware Delivery (2026-04-29)
• Marimo Advisory Details Enabled Exploits Within Hours (2026-04-27)

Primary sources

• NVD record
• CISA KEV catalog
• Nuclei template

What this record does not say

• No CVSS score from NVD.
• No affected package data.
• No patch identifier.

KEV and EPSS are re-checked daily. Record last updated 2026-08-11.