CVE-2025-41729: Modbus Protocol DoS Vulnerability

CVE-2025-41729 Overview

CVE-2025-41729 is a denial of service vulnerability that allows an unauthenticated remote attacker to disrupt device availability by sending a specially crafted Modbus read command. This vulnerability affects industrial control system (ICS) devices utilizing the Modbus protocol, enabling attackers to cause service interruptions without requiring any authentication credentials.

Critical Impact

Unauthenticated attackers can remotely crash affected industrial devices, potentially disrupting critical infrastructure operations and manufacturing processes.

Affected Products

• Industrial control system devices supporting Modbus protocol (specific products detailed in CERT VDE advisory VDE-2025-094)

Discovery Timeline

• 2025-11-24 - CVE-2025-41729 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-41729

Vulnerability Analysis

This vulnerability is classified under CWE-1287 (Improper Validation of Specified Type of Input), indicating that the affected device fails to properly validate input received through Modbus read commands. The flaw exists in how the device processes specially crafted Modbus read requests, allowing an attacker to trigger a denial of service condition.

The vulnerability is particularly concerning for industrial environments because Modbus is a widely deployed protocol in operational technology (OT) networks. The lack of authentication requirements means any network-connected attacker with access to the Modbus service can exploit this vulnerability without needing valid credentials.

Root Cause

The root cause stems from improper validation of specified input types (CWE-1287). The device does not adequately sanitize or validate the parameters within Modbus read commands before processing them. When a malformed or specially crafted read request is received, the device fails to handle the unexpected input gracefully, resulting in a crash or unresponsive state.

Attack Vector

The attack can be executed remotely over the network without any authentication or user interaction. An attacker needs network access to the target device's Modbus service (typically TCP port 502) to send the malicious read command. The attack complexity is low, making it feasible for attackers with minimal technical expertise to exploit.

The exploitation involves crafting a Modbus read command with specific malformed parameters that the device's parsing logic does not handle properly. When the device attempts to process this request, it triggers an exception or resource exhaustion that leads to denial of service.

For detailed technical information about the specific exploitation parameters, refer to the CERT VDE Security Advisory.

Detection Methods for CVE-2025-41729

Indicators of Compromise

• Unexpected device reboots or service interruptions without apparent cause
• Anomalous Modbus traffic patterns, particularly read commands with unusual register addresses or quantities
• Device logs showing parsing errors or exceptions related to Modbus command processing
• Network traffic containing malformed Modbus read requests targeting vulnerable devices

Detection Strategies

• Implement network intrusion detection systems (NIDS) with Modbus protocol awareness to identify malformed read commands
• Deploy deep packet inspection (DPI) at network boundaries to analyze Modbus traffic for anomalies
• Configure industrial firewalls to log and alert on unusual Modbus read request patterns
• Utilize SentinelOne Singularity for endpoint detection and response to monitor for exploitation attempts

Monitoring Recommendations

• Enable detailed logging on Modbus-capable devices to capture command-level activity
• Monitor device availability and establish baseline response times to detect degradation
• Set up alerts for repeated connection attempts from unauthorized IP addresses to Modbus services
• Implement network segmentation monitoring to detect lateral movement toward OT networks

How to Mitigate CVE-2025-41729

Immediate Actions Required

• Review the CERT VDE Security Advisory VDE-2025-094 for vendor-specific patch information
• Restrict network access to Modbus services using firewall rules and network segmentation
• Implement access control lists (ACLs) to limit which IP addresses can communicate with affected devices
• Consider deploying industrial protocol-aware firewalls to filter Modbus traffic

Patch Information

Consult the CERT VDE Security Advisory for the latest patch availability and vendor-specific remediation guidance. Organizations should contact their device vendor directly for firmware updates addressing this vulnerability.

Workarounds

• Isolate affected devices on a dedicated network segment inaccessible from untrusted networks
• Deploy network-level filtering to block Modbus traffic from unauthorized sources
• Implement a Modbus-aware proxy or gateway that can validate and sanitize read commands before forwarding
• Monitor affected devices continuously and configure automated restart procedures if service disruption is detected

# Example firewall rule to restrict Modbus access (iptables)
# Allow Modbus (TCP 502) only from trusted management subnet
iptables -A INPUT -p tcp --dport 502 -s 10.0.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 502 -j DROP