How severe is CVE-2026-39987?

CVE-2026-39987 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-39987 being actively exploited?

Yes. CVE-2026-39987 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2026-04-23, which means active exploitation has been confirmed. It should be prioritised for remediation.

What products are affected by CVE-2026-39987?

CVE-2026-39987 affects Coreweave Marimo. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-39987?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.

Does CVE-2026-39987 have an EU (EUVD) identifier?

Yes. CVE-2026-39987 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-20980. It is also flagged as exploited in the EUVD (since 2026-04-23).

When was CVE-2026-39987 published?

CVE-2026-39987 was published on 2026-04-09 and last updated on 2026-06-17.

CVE-2026-39987

CVE-2026-39987 is a critical-severity vulnerability in Coreweave Marimo with a CVSS 3.x base score of 9.8. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2026-04-23). The underlying weakness is classified as CWE-306.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v4: 9.3
EPSS exploit prediction: 96% (100th percentile)
Actively exploited: Yes — listed in CISA KEV (added 2026-04-23)
EU (EUVD) id: EUVD-2026-20980
EU exploitation: Flagged exploited in the ENISA EU Vulnerability Database (since 2026-04-23)
Weakness: CWE-306
Affected product: Coreweave Marimo
Published: 2026-04-09
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2026-39987?: 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.
How severe is CVE-2026-39987?: CVE-2026-39987 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-39987 being actively exploited?: Yes. CVE-2026-39987 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2026-04-23, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2026-39987?: CVE-2026-39987 affects Coreweave Marimo. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-39987?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2026-39987 have an EU (EUVD) identifier?: Yes. CVE-2026-39987 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-20980. It is also flagged as exploited in the EUVD (since 2026-04-23).
When was CVE-2026-39987 published?: CVE-2026-39987 was published on 2026-04-09 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:coreweave:marimo:*:*:*:*:*:python:*:*

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