CVE-2026-38719: OpENer Buffer Overflow Vulnerability

CVE-2026-38719 Overview

CVE-2026-38719 is an out-of-bounds read vulnerability in OpENer v2.3-558-g1e99582, an open-source EtherNet/IP (ENIP) stack implementation. The flaw resides in the Common Packet Format (CPF) parser, specifically within the CreateCommonPacketFormatStructure() function located in source/src/enet_encap/cpf.c. A crafted ENIP/CPF message can supply an attacker-controlled item_count value that is not consistently validated against the remaining data_length of the CPF slice. The vulnerability is tracked as [CWE-125: Out-of-bounds Read] and primarily affects availability.

Critical Impact
A locally reachable attacker can send a malformed ENIP/CPF message to trigger an out-of-bounds read, leading to a denial-of-service condition in the OpENer process.

Affected Products

OpENer EtherNet/IP stack version v2.3-558-g1e99582
Industrial control system (ICS) devices embedding the affected OpENer build
EtherNet/IP-enabled applications linking against the vulnerable CPF parser

Discovery Timeline

2026-05-18 - CVE-2026-38719 published to NVD
2026-05-18 - Last updated in NVD database

Technical Details for CVE-2026-38719

Vulnerability Analysis

The vulnerability resides in OpENer's Common Packet Format (CPF) parser. CPF is a sub-encapsulation layer used by EtherNet/IP (ENIP) to package multiple data items within a single message. When OpENer receives an ENIP packet containing a CPF payload, CreateCommonPacketFormatStructure() in source/src/enet_encap/cpf.c parses the item_count field followed by the corresponding item structures.

The parser reads the item_count value directly from the network buffer but does not consistently verify that the remaining data_length of the CPF slice can accommodate the declared number of items. When item_count exceeds the actual bytes available, subsequent reads access memory beyond the bounds of the input buffer.

The resulting out-of-bounds read produces undefined behavior, typically a process crash. Because OpENer is commonly deployed on embedded industrial controllers, a crash interrupts EtherNet/IP communications and disrupts process control operations.

Root Cause

The root cause is missing length validation between the attacker-supplied item_count field and the actual size of the CPF data slice. The parser trusts the declared count without cross-checking it against the bytes remaining in the buffer before iterating over item headers.

Attack Vector

Exploitation requires the attacker to deliver a crafted ENIP/CPF message to the vulnerable parser. The CVSS vector indicates a local attack vector with no privileges or user interaction required. An attacker reaching the EtherNet/IP listener with a malformed CPF payload can trigger the out-of-bounds read and crash the service. No verified public exploit is available at this time. Refer to the GitHub Issue #558 for technical discussion.

Detection Methods for CVE-2026-38719

Indicators of Compromise

Unexpected termination or repeated restarts of the OpENer process or ENIP-enabled service
ENIP packets on TCP/UDP port 44818 or UDP port 2222 containing a CPF item_count value inconsistent with the encapsulated payload length
Core dumps or segmentation faults referencing CreateCommonPacketFormatStructure in cpf.c

Detection Strategies

Deploy deep packet inspection signatures that flag ENIP/CPF messages where the declared item_count does not match the remaining payload size
Monitor process telemetry on ICS hosts for crashes of binaries linked against OpENer
Correlate ENIP traffic spikes from a single source with subsequent service restarts on affected devices

Monitoring Recommendations

Capture and baseline ENIP/CPF traffic on operational technology (OT) network segments to identify anomalous item_count distributions
Enable verbose logging on OpENer-based devices to record malformed encapsulation messages and parser errors
Forward ICS network and host telemetry to a centralized analytics platform for cross-source correlation

How to Mitigate CVE-2026-38719

Immediate Actions Required

Restrict access to EtherNet/IP listening ports so only authorized engineering workstations and controllers can reach the OpENer service
Audit deployed firmware and applications to identify components built on the affected OpENer revision
Apply patches from the upstream OpENer repository once a fixed commit is published and tracked in Issue #558

Patch Information

At the time of publication, no official fixed release has been listed in the NVD entry. Track the upstream OpENer project for a commit that enforces validation of item_count against the remaining CPF data_length in CreateCommonPacketFormatStructure(). Rebuild and redeploy affected firmware once the fix is available.

Workarounds

Segment OT networks and place EtherNet/IP devices behind industrial firewalls that enforce protocol-aware filtering
Use ENIP-aware intrusion prevention rules to drop CPF messages with inconsistent length fields before they reach vulnerable parsers
Disable the EtherNet/IP service on devices where it is not operationally required

bash

# Example firewall rule to limit ENIP access to authorized hosts
iptables -A INPUT -p tcp --dport 44818 -s <trusted_engineering_subnet> -j ACCEPT
iptables -A INPUT -p tcp --dport 44818 -j DROP
iptables -A INPUT -p udp --dport 2222 -s <trusted_engineering_subnet> -j ACCEPT
iptables -A INPUT -p udp --dport 2222 -j DROP