# [CRIT] [GHSA / CRITICAL] CVE-2026-46339: 9router: Unauthenticated Remote Code Execution via unprotected MCP custom plugin routes

**Source:** GitHub Security Advisories
**Published:** 2026-05-19
**Article:** https://github.com/advisories/GHSA-fhh6-4qxv-rpqj

## Threat Profile

9router: Unauthenticated Remote Code Execution via unprotected MCP custom plugin routes

## Summary

9router exposes two unauthenticated API endpoints that, when chained together, allow any network-adjacent attacker to execute arbitrary OS commands as the user running the 9router process — with **zero prerequisites** and **no credentials required**.

The vulnerability exists because the Next.js middleware that enforces authentication (`src/proxy.js`) only guards 8 explicitly listed routes. The a…

## Indicators of Compromise (high-fidelity only)

- **CVE:** `CVE-2026-46339`

## MITRE ATT&CK Techniques

- **T1190** — Exploit Public-Facing Application
- **T1021.002** — SMB/Windows Admin Shares
- **T1569.002** — Service Execution
- **T1219** — Remote Access Software
- **T1204.002** — User Execution: Malicious File
- **T1059.004** — Unix Shell
- **T1071.001** — Web Protocols
- **T1095** — Non-Application Layer Protocol

## Kill chain phases observed

_(none detected from narrative keywords)_

## Recommended hunts

### 9router unauthenticated RCE — POST /api/cli-tools/cowork-settings with customPlugins.command

`UC_251_4` · phase: **exploit** · confidence: **High** · AI-generated for this article

**Splunk SPL (CIM):**
```spl
| tstats summariesonly=true count, min(_time) as firstTime, max(_time) as lastTime from datamodel=Web.Web where Web.http_method=POST Web.url="*/api/cli-tools/cowork-settings*" by Web.src, Web.dest, Web.url, Web.http_method, Web.dest_port, Web.http_user_agent
| `drop_dm_object_name(Web)`
| where dest_port=20128 OR isnull(dest_port)
| convert ctime(firstTime) ctime(lastTime)
```

### 9router CVE-2026-46339 — GET /api/mcp/{plugin}/sse triggers stored command spawn()

`UC_251_5` · phase: **exploit** · confidence: **High** · AI-generated for this article

**Splunk SPL (CIM):**
```spl
| tstats summariesonly=true count, min(_time) as firstTime from datamodel=Web.Web where Web.http_method=GET Web.url="*/api/mcp/*/sse*" by Web.src, Web.dest, Web.url, Web.http_method, Web.dest_port, Web.http_user_agent
| `drop_dm_object_name(Web)`
| where dest_port=20128 OR isnull(dest_port)
| convert ctime(firstTime)
```

### 9router Node.js process spawning shell binary (CVE-2026-46339 post-exploit)

`UC_251_6` · phase: **install** · confidence: **High** · AI-generated for this article

**Splunk SPL (CIM):**
```spl
| tstats summariesonly=true count, min(_time) as firstTime, values(Processes.process) as cmdlines from datamodel=Endpoint.Processes where (Processes.parent_process_name=node OR Processes.parent_process_name="next-server" OR Processes.parent_process="*node*server.js*" OR Processes.parent_process="*9router*") (Processes.process_name=bash OR Processes.process_name=sh OR Processes.process_name=dash OR Processes.process_name=ash OR Processes.process_name=zsh) by Processes.dest, Processes.user, Processes.process_name, Processes.parent_process_name, Processes.process
| `drop_dm_object_name(Processes)`
| convert ctime(firstTime)
```

**Defender KQL:**
```kql
DeviceProcessEvents
| where Timestamp > ago(7d)
| where InitiatingProcessFileName =~ "node" or InitiatingProcessCommandLine has_any ("server.js","next-server","9router")
| where FileName in~ ("sh","bash","dash","ash","zsh","ksh")
| project Timestamp, DeviceName, AccountName,
          ParentImage = InitiatingProcessFolderPath,
          ParentCmd   = InitiatingProcessCommandLine,
          ChildImage  = FolderPath,
          ChildCmd    = ProcessCommandLine,
          SHA256
| order by Timestamp desc
```

### Reverse shell from 9router-spawned shell — outbound TCP from node-child bash

`UC_251_7` · phase: **c2** · confidence: **Medium** · AI-generated for this article

**Splunk SPL (CIM):**
```spl
| tstats summariesonly=true count, min(_time) as firstTime, values(All_Traffic.dest_port) as ports from datamodel=Network_Traffic.All_Traffic where (All_Traffic.app=bash OR All_Traffic.app=sh OR All_Traffic.app=dash OR All_Traffic.process_name=bash OR All_Traffic.process_name=sh) All_Traffic.dest_category!=internal by All_Traffic.src, All_Traffic.dest, All_Traffic.dest_port, All_Traffic.app, All_Traffic.process_name
| `drop_dm_object_name(All_Traffic)`
| convert ctime(firstTime)
```

**Defender KQL:**
```kql
DeviceNetworkEvents
| where Timestamp > ago(7d)
| where InitiatingProcessFileName in~ ("sh","bash","dash","ash","zsh")
| where InitiatingProcessParentFileName =~ "node"
   or InitiatingProcessCommandLine has_any ("/dev/tcp/","bash -i","nc -e")
| where RemoteIPType == "Public"
| project Timestamp, DeviceName,
          InitiatingProcessAccountName,
          InitiatingProcessFileName,
          InitiatingProcessCommandLine,
          InitiatingProcessParentFileName,
          RemoteIP, RemotePort, RemoteUrl, Protocol
| order by Timestamp desc
```

### Remote service execution — PsExec / SMB lateral movement

`UC_LATERAL_PSEXEC` · phase: **actions** · confidence: **High**

**Splunk SPL (CIM):**
```spl
| tstats `summariesonly` count min(_time) as firstTime max(_time) as lastTime
    from datamodel=Endpoint.Processes
    where Processes.process_name IN ("psexec.exe","psexesvc.exe","paexec.exe","smbexec.py")
       OR (Processes.process_name="wmic.exe" AND Processes.process="*/node:*")
    by Processes.dest, Processes.user, Processes.process_name, Processes.process, Processes.parent_process_name
| `drop_dm_object_name(Processes)`
```

**Defender KQL:**
```kql
DeviceProcessEvents
| where Timestamp > ago(7d)
| where AccountName !endswith "$"
| where FileName in~ ("psexec.exe","psexesvc.exe","paexec.exe","smbexec.py")
   or (FileName =~ "wmic.exe" and ProcessCommandLine has "/node:")
| project Timestamp, DeviceName, AccountName, FileName, ProcessCommandLine, InitiatingProcessFileName
| order by Timestamp desc
```

### RMM tool installed by non-IT user — remote-access utility for hands-on-keyboard

`UC_RMM_TOOLS` · phase: **install** · confidence: **High**

**Splunk SPL (CIM):**
```spl
| tstats `summariesonly` count min(_time) as firstTime max(_time) as lastTime
    from datamodel=Endpoint.Processes
    where Processes.process_name IN ("AnyDesk.exe","TeamViewer.exe","TeamViewer_Service.exe",
        "ScreenConnect.ClientService.exe","ConnectWiseControl.ClientService.exe",
        "atera_agent.exe","SplashtopStreamer.exe","RustDesk.exe","NinjaOne.exe","kaseya*.exe")
    by Processes.dest, Processes.user, Processes.process_name, Processes.process, Processes.parent_process_name
| `drop_dm_object_name(Processes)`
```

**Defender KQL:**
```kql
DeviceProcessEvents
| where Timestamp > ago(7d)
| where AccountName !endswith "$"
| where FileName in~ ("AnyDesk.exe","TeamViewer.exe","TeamViewer_Service.exe",
        "ScreenConnect.ClientService.exe","ConnectWiseControl.ClientService.exe",
        "atera_agent.exe","SplashtopStreamer.exe","RustDesk.exe","NinjaOne.exe")
   or FileName matches regex @"(?i)kaseya.*\.exe"
| project Timestamp, DeviceName, AccountName, FileName, ProcessCommandLine
```

### Article-specific behavioural hunt — [GHSA / CRITICAL] CVE-2026-46339: 9router: Unauthenticated Remote Code Execution

`UC_251_3` · phase: **exploit** · confidence: **High**

**Splunk SPL (CIM):**
```spl
``` Article-specific bespoke detection — [GHSA / CRITICAL] CVE-2026-46339: 9router: Unauthenticated Remote Code Execution ```
| tstats `summariesonly` count earliest(_time) AS firstTime latest(_time) AS lastTime
    from datamodel=Endpoint.Processes
    where (Processes.process_name IN ("next.js","poc.py"))
    by Processes.dest, Processes.user, Processes.process_name,
       Processes.process, Processes.parent_process_name, Processes.process_path
| `drop_dm_object_name(Processes)`
| `security_content_ctime(firstTime)`
| append [
| tstats `summariesonly` count
    from datamodel=Endpoint.Filesystem
    where Filesystem.action IN ("created","modified")
      AND (Filesystem.file_path="*/dev/tcp/ATTACKER_IP/4444*" OR Filesystem.file_path="*/dev/tcp/...*" OR Filesystem.file_path="*/tmp/pwned.txt*" OR Filesystem.file_path="*/dev/null*" OR Filesystem.file_name IN ("next.js","poc.py"))
    by Filesystem.dest, Filesystem.user, Filesystem.process_name,
       Filesystem.file_path, Filesystem.file_name
| `drop_dm_object_name(Filesystem)`
]
```

**Defender KQL:**
```kql
// Article-specific bespoke detection — [GHSA / CRITICAL] CVE-2026-46339: 9router: Unauthenticated Remote Code Execution
// Hunts the actual binaries / paths / commandline fragments named
// in the article instead of a generic technique-class template.
DeviceProcessEvents
| where Timestamp > ago(30d)
| where (FileName in~ ("next.js", "poc.py"))
| project Timestamp, DeviceName, AccountName, FileName,
          FolderPath, ProcessCommandLine,
          InitiatingProcessFileName, InitiatingProcessCommandLine
| order by Timestamp desc

// File-creation events for the named binaries / paths
DeviceFileEvents
| where Timestamp > ago(30d)
| where ActionType in ("FileCreated","FileModified")
| where (FolderPath has_any ("/dev/tcp/ATTACKER_IP/4444", "/dev/tcp/...", "/tmp/pwned.txt", "/dev/null") or FileName in~ ("next.js", "poc.py"))
| project Timestamp, DeviceName, AccountName, FolderPath,
          FileName, ActionType, InitiatingProcessFileName,
          InitiatingProcessCommandLine
| order by Timestamp desc
```

### IOC-driven hunts (use shared templates)

These are standard IOC-substitution hunts — the canonical SPL and KQL live once in [`_TEMPLATES.md`](../_TEMPLATES.md), so we don't repeat the same boilerplate on every CVE / hash / network-IOC briefing.

- **Asset exposure — vulnerability matches article CVE(s)** ([template](../_TEMPLATES.md#asset-exposure)) — phase: **recon**, confidence: **High**
  - CVE(s): `CVE-2026-46339`


## Why this matters

Severity classified as **CRIT** based on: CVE present, 8 use case(s) fired, 8 technique(s) inferred. Read the full article for actor attribution, tooling details, and any defanged IOCs in the body that aren't visible in the RSS summary.