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

# 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