Is CVE-2026-39987 actively exploited?

Yes. KEV Intelligence tracks CVE-2026-39987 as a known exploited vulnerability. Confidence is confirmed.

What exploitation activity has KEV Intelligence observed?

KEV Intelligence has not yet recorded sensor-observed exploitation attempts for CVE-2026-39987. Our sensors continue to monitor for activity targeting this CVE.

Which versions are affected?

CVE-2026-39987 affects marimo-team marimo. Reported affected version: < 0.23.0.

Yes. CVE-2026-39987 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. KEV Intelligence attested it 1 day ahead of CISA.

CVE-2026-39987 Exploited in the Wild — marimo

Q: How should organizations remediate it?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Q: Is it in CISA KEV?

Yes. CVE-2026-39987 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. KEV Intelligence attested it 1 day ahead of CISA.

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2026-39987 is an unauthenticated vulnerability affecting marimo-team marimo. marimo is a reactive Python notebook. Prior to 0.23.0, Marimo has a Pre-Auth RCE vulnerability. The terminal WebSocket endpoint...

Is it exploited?

Yes. KEV Intelligence tracks this CVE as a known exploited vulnerability. Confidence is confirmed.

Who is affected?

marimo-team / marimo affected before 0.23.0.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

marimo is a reactive Python notebook

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.

Vendor Product Affected Status

marimo-team marimo Before 0.23.0 Affected

Published: 09 Apr 2026
Exploitation Reported: 01 Jun 2026
Attack vector: Remote
Complexity: Low
Privileges: None
User interaction: None

CVE References

CVE Record CVE.org · CVE Record https://www.cve.org/CVERecord?id=CVE-2026-39987
https://github.com/marimo-team/marimo/security/advisories/GHSA-2679-6mx9-h9xc github.com · CVE Record https://github.com/marimo-team/marimo/security/advisories/GHSA-2679-6...
https://github.com/marimo-team/marimo/pull/9098 github.com · CVE Record https://github.com/marimo-team/marimo/pull/9098
https://github.com/marimo-team/marimo/commit/c24d4806398f30be6b12acd6c60d1d7c68cfd12a github.com · CVE Record https://github.com/marimo-team/marimo/commit/c24d4806398f30be6b12acd6...

Exploitation evidence

Why KEV Intelligence marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CVE

Recorded 01 Jun 2026

Independent exploitation attestation added to the KEV Intelligence record.

Proof of concept available

GitHub

Recorded 02 Jun 2026

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the KEV Intelligence Pro API.

Learn about Pro API access

Source	Added
CVE First	2026-06-01 13:23 UTC
CISA	2026-06-02 14:01 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets: 0
User-Agents: 0

Raw values available in Pro and Enterprise.

Scanner coverage

Nuclei template detected 01 Jun 2026.

View Nuclei template

Virtual patch status

No KEV Intelligence virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner	Reference	Detected
Nuclei	https://github.com/projectdiscovery/nuclei-templates/blob/main/javascript/cves/2026/CVE-2026-39987.yaml	01 Jun 2026

Risk and context

Severity, weaknesses, and research context

CVSS v4.0

9.3 Critical

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

EPSS

96.6%

Weaknesses

Missing Authentication for Critical Function CWE-306

Recent mention · Tenable Blog

The Agentic AI threat cluster: Seven incidents, three actors, and what they mean for your exposure

Tenable’s Research Special Operations (RSO) team has been tracking a cluster of agentic AI threat activity since late July 2026. The Taiwan autonomous AI cyber attack confirmed what the cluster data already showed: near-autonomous offensive AI has crossed from theoretical risk...

Read full advisory

All CVSS Scores

CVSS v4.0 9.3 Critical

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

CVSS v3.1 9.8 Critical

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

All Mentions

Recent mention · Tenable Blog

The Agentic AI threat cluster: Seven incidents, three actors, and what they mean for your exposure

Tenable Blog · 15 Aug 2026

Tenable’s Research Special Operations (RSO) team has been tracking a cluster of agentic AI threat activity since late July 2026. The Taiwan autonomous AI cyber attack confirmed what the cluster data already showed: near-autonomous offensive AI has crossed from theoretical risk to operational reality.Key TakeawaysTaiwan's Ministry of Digital Affairs confirmed a near-autonomous AI cyber attack in July 2026 in which autonomous agents mapped 21 connected government systems, compromised 85 accounts, and exfiltrated more than 2,564 personnel records in approximately four days.The Taiwan campaign...

Recent mention · DarkWebInformer

Root in One Request: Pre-Auth RCE in Marimo (CVE-2026-39987)

DarkWebInformer · 29 May 2026

CVE-2026-39987 is a critical pre-authentication remote code execution flaw in Marimo, a popular open-source reactive Python notebook framework and a modern alternative to Jupyter with roughly 19.6k GitHub stars.

Recent mention · TheHackerNews

Attackers Use LLM Agent for Post-Exploitation After Marimo CVE-2026-39987 Exploit

TheHackerNews · 29 May 2026

An unknown threat actor has been observed using a large language model (LLM) agent to conduct post-compromise actions after obtaining initial access following the exploitation of a publicly-accessible Marimo network using a recently disclosed vulnerability. "The attacker compromised an internet-reachable Marimo notebook via CVE-2026-39987, extracted two cloud credentials from the compromised

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

K3ysTr0K3R/CVE-2026-39987

github · Created 2026-08-19 18:53:43 UTC · 0 stars · AI assessment 90%

CVE-2026-39987 — Marimo Pre-Authentication RCE

MADA0L/CVE-2026-39987-Poc

github · Created 2026-08-10 02:08:03 UTC · 0 stars · AI assessment 85%

Proof of Concept (PoC) WebSocket client for CVE-2026-39987 (Marimo Pre-Auth RCE), intended for authorized security testing.

alreadyClosed/CVE-2026-39987

github · Created 2026-08-07 07:04:38 UTC · 0 stars · AI assessment 90%

CVE-2026-39987 for marimo 0.20.4 PoC

Wind010/CVE-2026-39987_PoC

github · Created 2026-08-03 06:32:49 UTC · 0 stars · AI assessment 90%

A proof-of-concept for CVE-2026-39987

vanhari/CVE-2026-39987

github · Created 2026-08-02 17:34:07 UTC · 0 stars · AI assessment 85%

jasonbernier/CVE-2026-39987

github · Created 2026-08-02 14:22:20 UTC · 0 stars · AI assessment 90%

Simple POC for CVE-2026-39987

marimo Pre-Auth RCE via Terminal WebSocket Authentication Bypass (/terminal/ws missing validate_auth)

pruva · Created 2026-07-30 07:54:02 UTC

Severity: CRITICAL | CVE: CVE-2026-39987 | Package: marimo

Marimo <= 0.20.4 - Pre-Auth Terminal WebSocket RCE

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation

12 Jun 2026
Public PoC available

Public proof-of-concept code published
02 Jun 2026
Added to CISA KEV

Listed in the CISA Known Exploited Vulnerabilities catalog
01 Jun 2026
Nuclei template available

Scanner coverage available
01 Jun 2026
Added to KEV Intelligence KEV Feed

High-confidence, third-party attested exploitation
09 Apr 2026
CVE published

Vulnerability disclosed publicly
08 Apr 2026
CVE ID reserved

Identifier reserved by the CNA

Pro API

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Evidence confidence and provenance
First-party sensor telemetry
PoC and scanner references
Affected versions and enrichment
Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2026-39987

Free JSON includes basic KEV fields

{
  "cve_id": "CVE-2026-39987",
  "confidence": "Confirmed",
  "cvss_score": 9.3,
  "cvss_estimated": false,
  "epss_score": 0.96576,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}

CVE-2026-39987

What security teams need to know first

marimo is a reactive Python notebook

Tags

CVE References

Why KEV Intelligence marks this CVE as exploited

Exploited in the wild

Proof of concept available

Known exploited vulnerability sources

Operational artifacts and observed signals

Observed signals

Scanner coverage

Virtual patch status

Scanner Artifacts

Severity, weaknesses, and research context

Weaknesses

The Agentic AI threat cluster: Seven incidents, three actors, and what they mean for your exposure

All CVSS Scores

All Mentions

Potential Proof of Concepts

From disclosure to observed exploitation

Public PoC available

Added to CISA KEV

Nuclei template available

Added to KEV Intelligence KEV Feed

CVE published

CVE ID reserved

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