Detect Marimo Remote Code Execution via Missing Authentication (CVE-2026-39987) in Google Chronicle
CVE-2026-39987 is a critical remote code execution vulnerability in the Marimo reactive notebook framework caused by missing authentication (CWE-306) for critical server-side functions. An unauthenticated remote attacker can invoke kernel execution endpoints to run arbitrary Python code in the context of the Marimo server process. This vulnerability is actively exploited in the wild and listed on the CISA KEV catalog.
MITRE ATT&CK
YARA-L Detection Query
rule CVE_2026_39987_Marimo_RCE {
meta:
author = "df00tech detection engineering"
description = "Detects potential exploitation of CVE-2026-39987 Marimo unauthenticated RCE"
severity = "CRITICAL"
priority = "HIGH"
events:
$e1.metadata.event_type = "PROCESS_LAUNCH"
re.regex($e1.principal.process.command_line, `(?i)(marimo)`)
$e2.metadata.event_type = "PROCESS_LAUNCH"
re.regex($e2.principal.process.command_line, `(?i)(subprocess\.run|os\.system|eval\(|exec\(|Popen|shell=True|__import__)`)
$e1.principal.hostname = $e2.principal.hostname
$e2.metadata.event_timestamp.seconds > $e1.metadata.event_timestamp.seconds
$e2.metadata.event_timestamp.seconds < $e1.metadata.event_timestamp.seconds + 120
condition:
$e1 and $e2
}Chronicle YARA-L 2.0 rule correlating Marimo process launch events with subsequent shell execution primitives on the same host within a two-minute window, indicating CVE-2026-39987 exploitation.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate Marimo notebook code that calls subprocess for data engineering tasks
- Internal tooling that wraps Marimo server and executes system commands as part of its workflow
- Development environments where developers test Marimo's Python execution API
Other platforms for CVE-2026-39987
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Unauthenticated Marimo Kernel RCE via HTTP POST
Expected signal: HTTP POST to Marimo port 2718 from loopback or external IP; new child process (sh or bash) spawned under the Marimo/Python process; creation of /tmp/marimo_rce_test.txt by the Marimo server user
- Test 2Marimo RCE Reverse Shell Simulation
Expected signal: Outbound TCP connection from Marimo Python process to loopback port 9999; /bin/sh spawned as child of Python under Marimo server; socket.connect syscall in audit logs
- Test 3Marimo Persistence via Cron Injection through RCE
Expected signal: subprocess.run executing bash crontab command as Marimo server user; crontab modification event in audit logs; new cron entry for the Marimo user account
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