Critical Vulnerability in Grandstream GXP1600 VoIP Phones Exposes Devices to Remote Code Execution Attacks

title: Suspicious Outbound Shell Connection Potential Grandstream RCE
id: 550c5a7e-8c6f-4d8a-b3e9-1a2b3c4d5e6f
status: experimental
description: Detects potential Remote Code Execution (RCE) on Grandstream GXP1600 VoIP phones by identifying outbound network connections initiated by shell processes or common embedded utilities. This behavior is indicative of a reverse shell established after exploiting the critical stack-based buffer overflow (CVE-2026-2329).
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-2329
author: Security Arsenal
date: 2026/04/06
logsource:
    category: network_connection
detection:
    selection_shell:
        Image|endswith:
            - '/sh'
            - '/bash'
            - '/busybox'
            - '/nc'
            - '/telnet'
    selection_connection:
        Initiated: 'true'
    filter_sip:
        DestPort: 5060
    condition: selection_shell and selection_connection and not filter_sip
falsepositives:
    - Legitimate administrative shell access (rare on VoIP phones)
    - Authorized network troubleshooting by administrators
level: high
tags:
    - attack.execution
    - attack.t1059.004
    - cve.2026.2329

---
title: Grandstream GXP1600 Web Service Spawning Shell
id: 660d6b8f-9d7g-5e9b-c4f0-2b3c4d5e6f70
status: experimental
description: Detects potential exploitation of the unauthenticated stack-based buffer overflow (CVE-2026-2329) in Grandstream GXP1600 series VoIP phones. The rule identifies the web management service spawning a shell or download utility, which indicates successful Remote Code Execution without authentication.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-2329
author: Security Arsenal
date: 2026/04/06
logsource:
    category: process_creation
detection:
    selection_shell:
        Image|endswith:
            - '/sh'
            - '/bash'
            - '/busybox'
            - '/wget'
            - '/curl'
            - '/tftp'
    selection_parent:
        ParentImage|contains:
            - 'httpd'
            - 'lighttpd'
            - 'web'
            - 'manager'
    condition: all of selection_*
falsepositives:
    - Legitimate administrative system maintenance via web interface (rare)
level: critical
tags:
    - attack.initial_access
    - attack.exploit_public_facilities
    - cve.2026.2329

// Hunt for CVE-2026-2329: Grandstream GXP1600 Unauthenticated Buffer Overflow Exploitation
// Detects potential exploitation by correlating large inbound payloads (buffer overflow attempt)
// sent to the web management interface with subsequent system reboots (crashes) on Grandstream devices.
let GrandstreamReboots = 
    Syslog
    | where ProcessName contains "Grandstream" or SyslogMessage contains "GXP1600"
    | where SyslogMessage has_any ("System Reboot", "System: Boot", "System Startup", "system is up")
    | project RebootTime = TimeGenerated, DeviceIP = IPAddress, SyslogMessage;
DeviceNetworkEvents
    | where LocalPort in (80, 443, 8089) // Common Grandstream Web UI / Management Ports
    | where Inbound == true
    | where ReceivedBytes > 3000 // Heuristic: Stack-based buffer overflows often require overly long payloads
    | project NetworkTime = TimeGenerated, DeviceIP = LocalIP, RemoteIP, RemotePort, ReceivedBytes, DeviceName
    | join kind=inner (GrandstreamReboots) on DeviceIP
    | where (RebootTime - NetworkTime) between (0s .. 5m) // Correlation: Crash occurred within 5 minutes of exploit packet
    | project NetworkTime, RebootTime, DeviceIP, DeviceName, RemoteIP, ReceivedBytes, SyslogMessage
    | order by NetworkTime desc

name: Hunt.Grandstream.GXP1600.CVE20262329
description: |
  Hunts for indicators of compromise related to CVE-2026-2329 (Buffer Overflow/RCE) 
  on Grandstream GXP1600 series VoIP phones. 
  This artifact checks for suspicious process spawning (web servers spawning shells),
  configuration file modifications, and anomalous network connections 
  indicative of reverse shells.

parameters:
  - name: WebProcesses
    default: httpd,lighttpd,webmgr,apache
  - name: SuspiciousShells
    default: /bin/sh,/bin/bash,/bin/busybox,nc,telnet,openssl

sources:
  - query: |
      -- Hunt 1: Process Anomaly Detection
      -- Detects if the web interface is spawning shell processes (RCE behavior)
      SELECT 
        Parent.Name AS ParentProcess,
        Parent.Pid AS ParentPid,
        Child.Name AS SuspiciousProcess,
        Child.Pid AS ChildPid,
        Child.Cmdline AS ProcessCommandLine,
        Child.Ctime AS CreationTime
      FROM pslist()
      LEFT JOIN pslist() AS Parent ON Child.Ppid = Parent.Pid
      WHERE 
        Child.Exe =~ SuspiciousShells OR Child.Name =~ SuspiciousShells
        AND Parent.Name =~ WebProcesses

  - query: |
      -- Hunt 2: File System Integrity Check
      -- Checks for critical Grandstream configuration files and recent modifications
      SELECT FullPath, Size, Mode, Mtime, Atime
      FROM glob(globs=[
        '/var/config/*', 
        '/etc/*version*', 
        '/www/*', 
        '/tmp/*'
      ])
      WHERE Mtime > now() - 7 * 24 * 3600 
      -- Filter for recently changed files within the last 7 days

  - query: |
      -- Hunt 3: Network Indicator Analysis
      -- Detects outbound reverse shells or unauthorized connections from shell processes
      SELECT 
        Pid, 
        RemoteAddr, 
        RemotePort, 
        State, 
        Process.Name AS ProcessName, 
        Process.Cmdline AS Cmdline
      FROM netstat()
      LEFT JOIN pslist() AS Process ON Pid = Process.Pid
      WHERE 
        State = 'ESTABLISHED'
        AND RemotePort > 1024 
        AND (Process.Exe =~ SuspiciousShells OR Process.Name =~ SuspiciousShells)

#!/bin/bash

# Critical Vulnerability Scanner: Grandstream GXP1600 Series (CVE-2026-2329)
# Threat: Unauthenticated Stack-based Buffer Overflow -> Remote Code Execution (RCE)
# Severity: CVSS 9.3 (Critical)
# Purpose: Scan local network segments to identify vulnerable GXP1600 devices, 
#          extract firmware versions, and identify devices requiring immediate patching.

# --- Configuration ---
# Define the network range to scan (CIDR notation).
# Modify this to match your corporate VoIP VLAN or subnet.
TARGET_SUBNET="192.168.1.0/24"

# Ports commonly used by Grandstream GXP1600 series for web management
# 80 (HTTP), 443 (HTTPS), 8089 (Alternative HTTP/HTTPS)
PORTS="80,443,8089"

echo "[+] Starting Vulnerability Assessment for CVE-2026-2329"
echo "[+] Target Network: $TARGET_SUBNET"
echo "[+] Searching for Grandstream GXP1600 series devices..."
echo "---------------------------------------------------------------"

# --- Step 1: Network Discovery ---
# Use Nmap to perform a fast scan on the specified subnet for open web ports.
# -p: Specifies ports
# --open: Only shows open ports
# -oG: Greppable output for easy parsing
# -T4: Faster execution
DISCOVERY_FILE=$(mktemp)
nmap -p "$PORTS" --open -oG - "$TARGET_SUBNET" > "$DISCOVERY_FILE"

# --- Step 2: Device Identification & Verification ---
# Iterate through the Nmap results to find potential VoIP phones
while read -r line; do
    # Extract IP address from the Nmap output (Column 2)
    IP=$(echo "$line" | awk '{print $2}')
    
    # Check if the line contains open ports (Status: Up)
    if [[ "$line" == *"Up"* ]]; then
        # Determine which port is open by parsing the Ports field
        # Format: Ports: 80/open/tcp//http///
        OPEN_PORT=$(echo "$line" | grep -oP 'Ports: \K\d+(?=/open)')
        
        if [ -n "$OPEN_PORT" ]; then
            # --- Step 3: Threat Detection (IOC & Version Check) ---
            # Attempt to fetch the device status page. 
            # Note: CVE-2026-2329 exploits unauthenticated endpoints. 
            # We query the web server to identify the Device Model and Firmware.
            
            PROTOCOL="http"
            if [ "$OPEN_PORT" == "443" ]; then
                PROTOCOL="https"
            fi
            
            URL="${PROTOCOL}://${IP}:${OPEN_PORT}"
            
            # Fetch page content (ignore self-signed certs with -k, timeout 3s)
            # We look for 'Grandstream' and 'GXP16' in the HTML to identify the specific vulnerable series.
            DEVICE_INFO=$(curl -s -k -m 3 "$URL" 2>/dev/null)

            # Regex check for "Grandstream" and Model "GXP16" (matches GXP1610, GXP1625, etc.)
            if echo "$DEVICE_INFO" | grep -qi "Grandstream" && echo "$DEVICE_INFO" | grep -qi "GXP16"; then
                
                # Extract Model Name
                MODEL=$(echo "$DEVICE_INFO" | grep -oP '(?<=<title>).*?(?=</title>)' | tr -d '\n' | awk '{print $1 $2}')
                
                # Extract Firmware Version
                # Grandstream usually displays firmware in the format "1.0.7.23"
                # We look for patterns resembling X.X.X.X associated with firmware strings
                FIRMWARE=$(echo "$DEVICE_INFO" | grep -oiP 'Firmware Version:\s*\K[\d.]+' | head -n 1)

                # --- Step 4: Reporting ---
                echo "[!] VULNERABLE DEVICE DETECTED (GXP1600 Series)"
                echo "    IP Address:    $IP"
                echo "    Port/Protocol: $OPEN_PORT/$PROTOCOL"
                echo "    Model:         $MODEL"
                
                if [ -n "$FIRMWARE" ]; then
                    echo "    Firmware:      $FIRMWARE"
                    echo "    Action Required:"
                    echo "    1. Compare firmware version against Grandstream Security Advisory for CVE-2026-2329."
                    echo "    2. If version is older than the patch, update immediately."
                    echo "    3. Restrict management access to the device via firewall (Block ports 80/443 from WAN)."
                else
                    echo "    Firmware:      Unable to parse automatically."
                    echo "    Action Required:"
                    echo "    1. Manually browse to $URL and verify firmware version."
                    echo "    2. Ensure device is patched against stack-based buffer overflow."
                fi
                echo "---------------------------------------------------------------"
            fi
        fi
    fi
done < "$DISCOVERY_FILE"

# --- Cleanup ---
rm "$DISCOVERY_FILE"
echo "[+] Scan Complete. If no devices are listed, ensure the subnet range is correct."