CVE-2024-8937: Modbus Authentication RCE Vulnerability

CVE-2024-8937 Overview

CVE-2024-8937 is a memory buffer vulnerability [CWE-119] disclosed by Schneider Electric on November 13, 2024. The flaw exists in the authentication handling of a Modbus-enabled product and allows an attacker to corrupt memory used during authentication. Successful exploitation requires an attacker to first execute a Man-in-the-Middle (MITM) attack on the Modbus communication channel, then send a crafted Modbus function call that triggers the memory corruption. The end result can be arbitrary code execution on the affected device.

Critical Impact
An attacker positioned between a Modbus client and server can send a crafted function call that corrupts authentication memory, leading to arbitrary code execution on the industrial device.

Affected Products

Schneider Electric Modbus-enabled product (see Schneider Electric Security Advisory SEVD-2024-317-03)
Specific model and firmware versions listed in the vendor advisory
Operational Technology (OT) environments using Modbus over TCP

Discovery Timeline

2024-11-13 - CVE-2024-8937 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-8937

Vulnerability Analysis

The vulnerability is classified under [CWE-119], Improper Restriction of Operations within the Bounds of a Memory Buffer. The affected device processes Modbus function calls involved in the authentication workflow without validating that input data stays within allocated memory bounds. An attacker who tampers with these fields on the wire can write beyond the intended buffer and overwrite adjacent memory structures that hold authentication state.

Because exploitation targets authentication memory specifically, a successful attack can bypass access controls and place attacker-controlled data into execution paths. The attack requires network positioning between the legitimate client and the device, but no valid credentials and no user interaction on the target.

The EPSS score of 0.586% indicates a low forecasted probability of exploitation in the next 30 days, but industrial control environments frequently lack the compensating controls that reduce risk in enterprise IT networks.

Root Cause

The root cause is missing bounds validation on data supplied through Modbus function calls that participate in authentication. Fields consumed during credential handling are copied into fixed-size buffers without length checks. An attacker who alters these fields mid-transit can overflow the buffer and modify authentication-related memory, including pointers and state variables that subsequent code trusts.

Attack Vector

Exploitation follows a two-stage pattern. First, the attacker establishes a MITM position on the Modbus network path, typically through ARP spoofing, rogue switch access, or compromise of an intermediate device in the OT segment. Second, the attacker intercepts an authentication exchange and injects a crafted Modbus function call whose payload exceeds the expected bounds of the authentication buffer. The malformed request triggers the out-of-bounds write and can redirect execution into attacker-supplied code.

No verified proof-of-concept code is publicly available. Refer to the Schneider Electric Security Advisory for details on affected function codes and payload structure.

Detection Methods for CVE-2024-8937

Indicators of Compromise

Unexpected ARP table changes on OT network segments carrying Modbus traffic
Modbus TCP sessions originating from unauthorized MAC or IP addresses
Malformed or oversized Modbus function requests targeting authentication-related function codes
Unexplained device restarts, watchdog resets, or firmware integrity alerts on affected controllers

Detection Strategies

Deploy passive OT network monitoring to baseline Modbus traffic patterns and alert on protocol anomalies
Inspect Modbus payloads for oversized fields in authentication function calls using deep packet inspection
Correlate Layer 2 anomalies (ARP spoofing, MAC flapping) with Modbus session events in the same timeframe
Alert on any new device inserting itself into established Modbus client-server flows

Monitoring Recommendations

Continuously monitor east-west traffic on OT segments and log all Modbus function calls to a centralized data lake
Track device firmware versions and authentication failure rates to identify tampered controllers
Forward OT network telemetry to a SIEM for cross-domain correlation with IT-side reconnaissance activity

How to Mitigate CVE-2024-8937

Immediate Actions Required

Apply the firmware update published in Schneider Electric Security Advisory SEVD-2024-317-03 to all affected devices
Verify that Modbus traffic traverses only trusted, segmented network paths
Enable static ARP entries or ARP inspection on switches carrying Modbus traffic to block MITM prerequisites
Audit which engineering workstations and HMIs have Modbus access to affected controllers and restrict to the minimum set

Patch Information

Schneider Electric has published remediation guidance in advisory SEVD-2024-317-03. Consult the advisory for exact firmware versions, affected product references, and update procedures. Where an immediate patch is not feasible, apply the compensating controls in the advisory.

Workarounds

Isolate affected devices behind an industrial firewall configured to allow Modbus only from designated engineering hosts
Enforce port security and 802.1X on switches connecting Modbus devices to prevent unauthorized network insertion
Disable or block Modbus TCP on the device where it is not required for operations
Use encrypted tunnels (IPsec or VPN) between Modbus clients and servers to defeat MITM interception

bash

# Example firewall rule to restrict Modbus TCP (port 502) to trusted engineering host
iptables -A INPUT -p tcp --dport 502 -s <engineering_workstation_ip> -j ACCEPT
iptables -A INPUT -p tcp --dport 502 -j DROP