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CVE-2026-39987: Marimo Missing Authentication (CVSS 9.3)

CVE-2026-39987 is a critical severity missing authentication in Marimo with a CVSS score of 9.3. It is listed in the CISA Known Exploited Vulnerabilities catalog, so treat it as an active threat and patch immediately.

Last updated: Jun 17, 2026

Quick answer

Direct answer

CVE-2026-39987 is a critical severity missing authentication in Marimo with a CVSS score of 9.3. It is listed in the CISA Known Exploited Vulnerabilities catalog, so treat it as an active threat and patch immediately.

Risk scores

CVSS base score
9.3CRITICAL
EPSS probability
37.87%
Higher than 99 percent of all CVEs
CISA KEV
Exploited Yes
Added Apr 23, 2026
CVSS metricWhat it means
Attack vector (AV:N)Network: reachable remotely
Attack complexity (AC:L)Low complexity
Attack requirements (AT:N)No attack requirements
Privileges required (PR:N)No privileges required
User interaction (UI:N)No user interaction
Confidentiality (VC:H)High confidentiality impact
Integrity (VI:H)High integrity impact
Availability (VA:H)High availability impact

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

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.

About Marimo

CVE-2026-39987 affects Marimo, a product from Marimo. Before acting, confirm where Marimo runs in your estate, who owns it and whether it is reachable from the internet, because exposure decides real risk more than the score alone.

What the flaw is

In plain terms: 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.

The weakness class is Missing Authentication. A critical function can be used without logging in.

Based on its CVSS vector, the flaw can be reached over the network, needs no login, and needs no user interaction. It is listed in the CISA Known Exploited Vulnerabilities catalog, so treat it as an active threat and patch immediately.

Affected versions and timeline

FieldDetail
ProductMarimo
Affected versionsMarimo before 0.23.0
PublishedApr 9, 2026
Last modifiedJun 17, 2026
Added to CISA KEVApr 23, 2026
Assigning CNAsecurity-advisories@github.com

How to detect it

  • Inventory every instance of Marimo and record the running version against the affected range above.
  • Check external attack surface scans for internet facing instances of the component.
  • Review logs on affected systems for unusual requests, errors or new processes around the vulnerable function.
  • Confirm with an authenticated vulnerability scan once your scanner has a check for this CVE.

How to fix it

  • Apply the fixed version of Marimo named in the vendor advisory.
  • If patching must wait, restrict network access to the affected service and put it behind authentication or a web application firewall rule.
  • Rescan after the change to prove the exposure is gone, then close the ticket.

CTEM action plan

CTEM stageWhat to do for this CVE
ScopeAdd every business service that depends on Marimo to the current CTEM cycle.
DiscoverFind all instances, including shadow and cloud deployments, and record versions and exposure.
PrioritizeKnown exploited, so top priority.
ValidateConfirm the flaw is reachable and exploitable in your environment and that compensating controls work.
MobilizeAssign the fix to the asset owner with a due date matched to the priority, then verify closure.

CWE References

Technical References

Frequently asked questions

CVE-2026-39987 is a critical severity missing authentication in Marimo with a CVSS score of 9.3. It is listed in the CISA Known Exploited Vulnerabilities catalog, so treat it as an active threat and patch immediately.

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