CVE-2024-37039: Schneider Electric Sage RTU DoS Flaw

CVE-2024-37039 Overview

CVE-2024-37039 is a denial of service vulnerability affecting Schneider Electric Sage Remote Terminal Unit (RTU) firmware. The flaw is categorized as [CWE-252] Unchecked Return Value. An unauthenticated attacker can send a specially crafted HTTP request to trigger the condition and render the device unresponsive. Sage RTUs are deployed in electric, water, and gas utility substations, so loss of availability can disrupt operational technology (OT) processes. The vulnerability requires no privileges and no user interaction, and it can be reached over the network.

Critical Impact
A single crafted HTTP request can cause denial of service against Schneider Electric Sage RTU devices used in critical infrastructure environments.

Affected Products

Schneider Electric Sage RTU Firmware
Schneider Electric Sage 1410, Sage 1430, Sage 1450
Schneider Electric Sage 2400, Sage 3030 Magnum, Sage 4400

Discovery Timeline

2024-06-12 - CVE-2024-37039 published to the National Vulnerability Database
2024-06-12 - Schneider Electric publishes security notice SEVD-2024-163-05
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-37039

Vulnerability Analysis

The vulnerability resides in the HTTP request handling logic of the Sage RTU firmware. The implementation invokes a function whose return value is not checked before subsequent operations continue. When an attacker submits a crafted HTTP request that forces the underlying call to fail, the firmware proceeds without acknowledging the failure. Subsequent processing then operates on an invalid state, which causes the device to enter a denial of service condition.

Sage RTUs act as front-end controllers between SCADA masters and field instrumentation. Loss of availability interrupts telemetry collection, command execution, and protection coordination on the segments they manage. Recovery typically requires a manual restart of the device, which extends the outage window.

Root Cause

The root cause is a missing return value check, classified as [CWE-252]. Secure coding practice requires that every error-returning function be inspected before its results are consumed. In this firmware path, an unchecked failure allows downstream code to dereference or act upon uninitialized or invalid data, terminating the HTTP service or the device process.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker with reachability to the device HTTP service issues a specially crafted request that triggers the failure path. Because Sage RTUs are commonly deployed in flat OT network segments, any host with routing access to the management interface can deliver the payload.

// No verified proof-of-concept code is publicly available.
// Refer to Schneider Electric security notice SEVD-2024-163-05 for technical details.

Detection Methods for CVE-2024-37039

Indicators of Compromise

Unexpected reboots or HTTP service crashes on Sage 1410, 1430, 1450, 2400, 3030 Magnum, or 4400 RTUs
Loss of SCADA polling responses correlated with inbound HTTP traffic to the RTU management interface
Anomalous HTTP requests sourced from non-engineering workstations targeting RTU IP addresses

Detection Strategies

Monitor for malformed or non-standard HTTP requests directed at Sage RTU management ports
Alert on RTU availability gaps using ICMP, SNMP, or SCADA heartbeat polling
Correlate firewall logs at the IT/OT boundary for unauthorized HTTP sessions reaching substation devices

Monitoring Recommendations

Deploy passive OT network monitoring to baseline normal HTTP traffic to and from Sage RTUs
Forward syslog and SNMP traps from the RTUs and upstream firewalls into a centralized analytics platform
Track repeated session resets or process restarts on the RTU as availability indicators

How to Mitigate CVE-2024-37039

Immediate Actions Required

Apply the firmware update referenced in Schneider Electric notice SEVD-2024-163-05
Restrict network access to the RTU HTTP service to a dedicated engineering management VLAN
Inventory all Sage RTU models in service and verify firmware versions against the advisory

Patch Information

Schneider Electric has published remediation guidance in security notice SEVD-2024-163-05. Review the Schneider Electric Security Notice for fixed firmware versions, upgrade procedures, and compatibility considerations for each Sage RTU model.

Workarounds

Place Sage RTUs behind an industrial firewall and permit HTTP only from authorized engineering hosts
Disable the HTTP service on the RTU where operationally feasible and rely on dedicated engineering protocols
Enforce segmentation between corporate IT networks and OT substation networks following IEC 62443 zone and conduit principles

bash

# Example ACL restricting HTTP access to an authorized engineering subnet
access-list 110 permit tcp 10.10.20.0 0.0.0.255 host <RTU_IP> eq 80
access-list 110 deny   tcp any host <RTU_IP> eq 80
access-list 110 permit ip any any