CVE-2026-10703: OpENer Use After Free Vulnerability

CVE-2026-10703 Overview

CVE-2026-10703 is a use-after-free vulnerability in EIPStackGroup OpENer up to version 2.3.0, an open-source EtherNet/IP stack used in industrial control systems. The flaw resides in the CreateMessageRouterRequestStructure function within cipmessagerouter.c, part of the SendRRData Handler component. A remote attacker with low privileges can trigger the condition over the network without user interaction. A public proof-of-concept exists, and the project has been notified through an issue report but has not yet responded.

Critical Impact
Remote attackers can exploit the use-after-free condition in the SendRRData Handler to compromise the integrity, confidentiality, and availability of OpENer-based EtherNet/IP devices.

Affected Products

EIPStackGroup OpENer versions up to and including 2.3.0
Component: cipmessagerouter.c (SendRRData Handler)
Function: CreateMessageRouterRequestStructure

Discovery Timeline

2026-06-03 - CVE-2026-10703 published to the National Vulnerability Database (NVD)
2026-06-03 - Last updated in NVD database

Technical Details for CVE-2026-10703

Vulnerability Analysis

The vulnerability is classified as a use-after-free condition [CWE-119] affecting the EtherNet/IP message routing layer of OpENer. The CreateMessageRouterRequestStructure function in cipmessagerouter.c parses incoming Common Industrial Protocol (CIP) message router requests delivered through the SendRRData service. Improper lifetime management of a request structure allows the code to reference memory after it has been freed.

Remote attackers can craft malformed SendRRData packets targeting the EtherNet/IP listener to trigger the dangling pointer access. Successful exploitation may cause memory corruption, process crashes, or in some scenarios influence control flow. Because OpENer is widely embedded into programmable logic controllers (PLCs), drives, and remote I/O devices, the exposure extends into operational technology (OT) environments.

Root Cause

The root cause is improper management of object lifetime during CIP message router request parsing. The function continues to use a pointer to a request structure after the underlying memory has been released, producing a use-after-free condition. The bug originates in CreateMessageRouterRequestStructure and is reachable through the SendRRData encapsulation command.

Attack Vector

The attack vector is network-based. An attacker sends a specially crafted EtherNet/IP SendRRData message containing a malformed CIP message router request to the target device's listening port. The vulnerability has been publicly disclosed along with a proof-of-concept archive referenced in GitHub Issue #566 and the associated GitHub PoC Attachment.

No verified exploit code is reproduced here. Refer to the upstream GitHub OpENer Repository and VulDB CVE-2026-10703 entry for additional technical detail.

Detection Methods for CVE-2026-10703

Indicators of Compromise

Unexpected crashes or restarts of OpENer-based EtherNet/IP services on industrial endpoints
Inbound EtherNet/IP traffic on TCP/UDP port 44818 containing malformed SendRRData encapsulation requests
Repeated CIP message router requests from a single source preceding device instability

Detection Strategies

Deploy deep packet inspection on OT network segments to flag malformed EtherNet/IP SendRRData payloads targeting the CIP message router
Monitor process telemetry on devices running OpENer for abnormal terminations or restarts of the EtherNet/IP daemon
Correlate network anomalies against known PoC traffic patterns referenced in the VulDB Vulnerability #368016 entry

Monitoring Recommendations

Enable continuous logging of EtherNet/IP session establishment and SendRRData command frequency per source
Alert on repeated CIP parsing failures or stack faults reported by OpENer-based devices
Baseline normal CIP traffic patterns between engineering workstations and PLCs to identify deviations

How to Mitigate CVE-2026-10703

Immediate Actions Required

Inventory all devices and firmware embedding the OpENer EtherNet/IP stack version 2.3.0 or earlier
Restrict network reachability of EtherNet/IP services (port 44818) to authorized engineering hosts only
Subscribe to the GitHub OpENer Repository for upstream commits addressing the issue

Patch Information

At the time of publication, the EIPStackGroup OpENer project had been notified through GitHub Issue #566 but had not yet released an official fix. Asset owners should track the upstream repository for a patch addressing the use-after-free in CreateMessageRouterRequestStructure. Vendors that integrate OpENer into commercial products should be contacted for downstream firmware updates.

Workarounds

Segment OT networks and place OpENer-based devices behind industrial firewalls that filter CIP traffic
Disable the EtherNet/IP service on devices where it is not operationally required
Apply allow-list rules restricting SendRRData requests to known engineering workstation IP addresses
Use intrusion prevention signatures to drop malformed CIP message router requests on perimeter and east-west OT segments

bash

# Example firewall rule restricting EtherNet/IP (port 44818) to a trusted engineering host
iptables -A INPUT -p tcp --dport 44818 -s 10.10.5.20 -j ACCEPT
iptables -A INPUT -p udp --dport 44818 -s 10.10.5.20 -j ACCEPT
iptables -A INPUT -p tcp --dport 44818 -j DROP
iptables -A INPUT -p udp --dport 44818 -j DROP