Vulnerability report

Active exploitation observed Confirmed confidence In CISA KEV

CVE-2026-39987

marimo Affected by Pre Auth Remote Code Execution

Marimo-team / marimo · affected before 0.23.0

Watch CVE-2026-39987 Browse KEV feed
Severity
CVSS 9.3 · Critical
Confidence
Confirmed
Exploit status
Observed in sensors
EPSS
37.9%
First observed
23 Jul 2026
Last observed
29 Sep 2026

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. Previdian sensors observed exploitation attempts with confirmed confidence. Listed in CISA KEV. Also confirmed by third-party sources.

Who is affected?

Marimo-team / marimo affected before 0.23.0.

What should we do?

Patch immediately, validate internet-facing exposure, and monitor for matching requests.

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.

marimo-team Affected
marimo
Before 0.23.0
Published
09 Apr 2026
Exploitation Reported
01 Jun 2026
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

cisa nuclei_scanner python

CVE References

Exploitation evidence

Why Previdian 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

A trusted third party reported exploitation.

Active exploitation observed

Previdian sensor

First observed 23 Jul 2026

Previdian first observed exploitation attempts targeting this vulnerability in our honeypot sensors.

Proof of concept available

Nuclei Templates

Recorded 12 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 Previdian Pro API.

Learn about Pro API access
Source Added
CVE First 2026-06-01 13:23 UTC
CISA 2026-06-02 14:01 UTC
Previdian Sensors 2026-09-15 13:27 UTC

Operational indicators for this CVE are listed under Detection.

Sensor telemetry

First-party evidence of exploitation activity

Previdian sensors recorded exploitation attempts targeting this vulnerability. The cards and chart show volume, unique attackers, and daily activity.

3

Attempts observed

2

Unique attacker IPs

2

Attacker countries

NL · SG

3

Sensors observed

CVE-2026-39987 exploitation attempts over the last 80 days

Daily events observed by Previdian sensors

Updated 09 Oct 2026

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22 Jul 7 Aug 23 Aug 8 Sep 9 Oct

First observed 23 Jul 2026 · Last observed 29 Sep 2026

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Detection

Operational artifacts and observed signals

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

Observed signals

Request targets
User-Agents
Callback hosts
1
1
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Virtual patch status

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

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Attacker IP Indicators

Attacker IP indicators observed · available in Pro and Enterprise.

Sensor-derived attacker IP indicators are available to Pro and Enterprise accounts under Detection and through the Pro API.

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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

Potential damage if exploited. Separate from whether attackers are using it.

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

37.9%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Missing Authentication for Critical Function CWE-306

Recent mention · The Hacker News

Human Attacker Exploits Marimo RCE, Reaches SSH Bastion in Eight Seconds

With artificial intelligence (AI) shrinking the window between vulnerability discovery and exploitation and lowering the barrier to entry for bad actors, new findings from Sysdig show that skilled human operators can move just as swiftly after gaining initial access. In one...

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 · The Hacker News

Human Attacker Exploits Marimo RCE, Reaches SSH Bastion in Eight Seconds

The Hacker News · 15 Sep 2026

With artificial intelligence (AI) shrinking the window between vulnerability discovery and exploitation and lowering the barrier to entry for bad actors, new findings from Sysdig show that skilled human operators can move just as swiftly after gaining initial access. In one instance highlighted by the cloud security company, the threat actor pivoted from a vulnerable Marimo notebook to an SSH

Recent mention · RecordedFuture

August 2026 CVE Landscape

RecordedFuture · 08 Sep 2026

In August 2026, Insikt Group® identified 73 high-impact vulnerabilities that should be prioritized for remediation, 43 of which had a Very Critical Recorded Future Risk Score. This represents a 14% decrease from last month.

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 · The Hacker News

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

The Hacker News · 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.

Industri4l-H3ll-Xpl0it3rs/CVE-2026-39987-Marimo-RCE

github · Created 2026-10-05 15:48:26 UTC · 0 stars · AI assessment 90%

CVE-2026-39987 Exploit | by infrar3d

mfahdk/CVE-2026-39987_RCE_PoC

github · Created 2026-09-20 12:40:18 UTC · 0 stars · AI assessment 90%

julichaan/CVE-2026-39987_POC

github · Created 2026-09-11 18:29:42 UTC · 0 stars · AI assessment 90%

Marimo WS Preauth RCE

Th3Purge/CVE-2026-39987

github · Created 2026-09-08 19:44:20 UTC · 1 stars · AI assessment 90%

Marimo Pre Authentication RCE

stapat1245/CVE-2026-39987-PoC

github · Created 2026-09-07 20:09:31 UTC · 0 stars · AI assessment 90%

CVE-2026-39987 Proof of Concept

Ghxstsec/CVE-2026-39987

github · Created 2026-09-01 21:40:03 UTC · 0 stars · AI assessment 90%

dodeepsink/CVE-2026-39987.py

github · Created 2026-08-20 19:25:00 UTC · 0 stars · AI assessment 85%

This python script exploit the vulnerable marimo /terminal/ws endpoint and returns a interactive shell.

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 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

  1. 13:01 UTC

    Indicators of compromise added (2)

    Indicators of compromise recorded

  2. 13:01 UTC

    Observed by Previdian sensors

    Evidence-backed exploitation signal

  3. 14:21 UTC

    Public PoC available

    Public proof-of-concept code published

  4. 14:01 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  5. 15:34 UTC

    Nuclei template available

    Scanner coverage available

  6. 13:23 UTC

    Added to Previdian KEV Feed

    High-confidence, third-party attested exploitation

  7. 17:16 UTC

    CVE published

    Vulnerability disclosed publicly

  8. 00:01 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

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Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
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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": 0.37865,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": true
  },
  "sensor_telemetry": { "attempts": 3, "sensors": 3 }
}