CVE-2026-39987 KEVPublic exploit Critical · 9.8 EPSS 99.6%

Marimo Remote Code Execution Vulnerability

Marimo · Marimo

Summary

The Marimo reactive Python notebook, prior to 0.23.0, has a missing authentication check on its terminal WebSocket endpoint /terminal/ws, which only verifies running mode and platform support before accepting connections. An unauthenticated remote attacker can connect to this endpoint to obtain a full PTY shell and execute arbitrary system commands, requiring no privileges or user interaction.

Official description · NVD

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.

Breakdown

74.8 / 100

Exploited: Yes, in CISA KEV
Reports: 0
Tactics: 2/15

How an attack unfolds

Based on mappings. Select a step to see the evidence.

How attackers get in
- Break in through an internet-facing appT1190 · Exploit Public-Facing ApplicationAI-written (claude-haiku-5-5)Medium confidence149 general detection rules
What they do
- Run commands on the systemT1059 · Command and Scripting InterpreterAI-written (claude-haiku-5-5)Medium confidence95 general detection rules

First seen exploited the day it was disclosed. Public exploit code (PoC-in-GitHub) appeared 3 days after disclosure.

DisclosedFirst seen exploitedVulnCheck KEV evidence9 Apr 2026day 0
Public exploit codePoC-in-GitHub12 Apr 2026+3 days
Added to CISA KEVEU database agrees23 Apr 2026+14 days

CISA KEV listing is when exploitation was confirmed, not necessarily the first attack.

2 fixes in marimo over 10 weeks. The latest fix listed for marimo is 0.23.9.

Fixes in marimoPyPI package, by fixed version. Earlier and later fixes in the same package, not necessarily the same bug.

0.23.0CVE-2026-399879 Apr 2026KEV
0.23.9CVE-2026-5438617 Jun 2026Latest listed

techniques

2 , grouped by in kill-chain order, 2 cited passages 2

Initial AccessTA0001

Exploit Public-Facing Application T1190 Medium

AI mapping from the description · how it is exploited

Unauthenticated network exploitation of public-facing endpoint

The terminal WebSocket endpoint /terminal/ws lacks authentication validation

From the official description (NVD) Original ↗

ExecutionTA0002

Command and Scripting Interpreter T1059 Medium

AI mapping from the description · primary impact

Full PTY shell enables arbitrary command execution

allowing an unauthenticated attacker to obtain a full PTY shell and execute arbitrary system commands

From the official description (NVD) Original ↗

Detection

0 rules for this CVE · 244 general rules for its techniques

Rules for this CVE

0 that reference CVE-2026-39987 directly.

CVE-specific rules are not available in this build. Search SigmaHQ ↗

General rules for this CVE’s techniques

These detect the technique in general, not this specific vulnerability.

Exploit Public-Facing ApplicationT1190149 general rules

Arcadyan Router Exploitationscriticaltest
Citrix ADS Exploitation CVE-2020-8193 CVE-2020-8195criticaltest
Citrix Netscaler Attack CVE-2019-19781criticaltest
Confluence Exploitation CVE-2019-3398criticaltest
CVE-2010-5278 Exploitation Attemptcriticaltest
CVE-2020-0688 Exchange Exploitation via Web Logcriticaltest
CVE-2020-10148 SolarWinds Orion API Auth Bypasscriticaltest
CVE-2020-5902 F5 BIG-IP Exploitation Attemptcriticaltest

All 149 on SigmaHQ ↗

Command and Scripting InterpreterT105995 general rules

HackTool - Sliver C2 Implant Activity Patterncriticaltest
Lazarus Group Activitycriticaltest
REvil Kaseya Incident Malware Patternscriticaltest
Turla Group Lateral Movementcriticaltest
Windows Defender AMSI Trigger Detectedhighstable
Windows Defender Threat Detectedhighstable
Abusable DLL Potential Sideloading From Suspicious Locationhightest
Add Insecure Download Source To Wingethightest

All 95 on SigmaHQ ↗

Sigma rules © SigmaHQ, Detection Rule License 1.1; linked, not reproduced.

Am I affected? What do I upgrade to?

From GitHub Security Advisories and OSV

1 package in 1 ecosystem. Main package: marimo.

PyPImarimoGHSA-2679-6mx9-h9xc PYSEC-2026-407

Upgrade to 0.23.0 or later

pippip install "marimo>=0.23.0"

The first fix for CVE-2026-39987. No other CVE tracked by Patchfirst affects this package.

Affected versions

If you run	Upgrade to
All versions before 0.23.0	0.23.0

“Up to” means the second version is the fix and is not affected.

Check your lockfile against all CVEs

What security researchers reported

Not named in any threat report yet

Also mentioned in 50 community threat pulses (AlienVault OTX)

Weaker evidence

Pulses are indicator collections that anyone can publish. A mention is not confirmation of exploitation.

Actively_Exploited_Kev | Oct 31, 202630 Oct 2026
Actively_Exploited_Kev | Oct 30, 202629 Oct 2026
Actively_Exploited_Kev | Oct 29, 202628 Oct 2026
Actively_Exploited_Kev | Oct 28, 202627 Oct 2026
Actively_Exploited_Kev | Oct 27, 202626 Oct 2026
Actively_Exploited_Kev | Oct 24, 202623 Oct 2026
44 more on OTX

References

5 links, grouped by NVD tag

Exploitation evidence

Exploited in the wild

Listed since 23 Apr 2026. Federal due date 7 May 2026. No recorded ransomware use.

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

ENISA

Marked exploited since 23 Apr 2026. EUVD-2026-20980

Marimo 0.20.4 - RCEEDB-52673 · webapps · multiple · 2026-09-02

, 30 Oct 2026

99.6%Top 0.05%

Chance of exploitation in the next 30 days. of scored CVEs (riskier than 99.95%).

3.1

9.8Critical · 9.8

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

Priority factorsFormula

In a KEV cataloglisted in CISA KEV and VulnCheck KEV 35.0/35

Recent KEV listingadded 205 days ago 5.0/10

Known ransomware usenot known 0.0/10

EPSS percentilepercentile 0.9995 20.0/20

Threat reports0 reports 0.0/10

Public exploit code2 NVD references tagged Exploit; 1 Exploit-DB entry; 26 PoC-in-GitHub repos; 1 nuclei template 5.0/5

Mentioned in OTX pulses50 pulses 3.0/3

CVSS base scorebase score 9.8 6.9/7

End-of-life productsupported or unknown 0.0

Total74.8

Record

Published: 9 Apr 2026
Modified: 17 Jun 2026
: CWE-306 Missing Authentication for Critical Functionality
Elsewhere: NVD CVE.org KEV JSON

How an attack unfolds

1How attackers get in

2What they do

Exploitation timelineExploitation timelineDated milestones for a CVE: when it was disclosed, when exploit code became public, when exploitation was confirmed, and when threat reports named it.

Patch historyPatch historyEarlier and later CVEs in the same code, in date order. It shows when a fix was bypassed or incomplete and which version finally fixed it.

Fixes in marimoPyPI package, by fixed version. Earlier and later fixes in the same package, not necessarily the same bug.

ATT&CKMITRE ATT&CKA public catalogue of the techniques attackers use, maintained by MITRE. Patchfirst uses it to describe what attackers do with a vulnerability. techniques

Initial AccessTA0001

ExecutionTA0002

Detection

Rules for this CVE

General rules for this CVE’s techniques

Am I affected? What do I upgrade to?

Affected versions

What security researchers reported

Also mentioned in 50 community threat pulses (AlienVault OTX)

References

Vendor Advisory 1

Patch 2

US Government Resource 1

Third Party Advisory 1

How attackers get in

What they do

techniques