Out-of-Bounds Read in EIPStackGroup OpENer

Executive Summary

CVE-2026-51537 is an out-of-bounds read vulnerability in EIPStackGroup OpENer version 2.3.0 (commit 76b95cf). The issue occurs in the Connection Manager when handling ForwardOpen requests.

An attacker can exploit this by sending a valid ENIP (EtherNet/IP) outer frame that contains a malformed CIP (Common Industrial Protocol) ForwardOpen or LargeForwardOpen request. The parser continues reading fields even when the request data is insufficient, leading to an out-of-bounds read.

This vulnerability is remotely triggerable over a network and does not require authentication, meaning any attacker with network access to the affected system can exploit it.

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Detection Guidance

Detecting this vulnerability on your network or system involves monitoring for malformed CIP ForwardOpen or LargeForwardOpen requests within ENIP traffic. Since the issue is triggered by short malformed packets, you can use network monitoring tools to inspect ENIP/CIP traffic for anomalies.

• Use Wireshark or tcpdump to capture ENIP traffic on the network. Filter for ENIP packets (port 44818) and inspect the CIP ForwardOpen/LargeForwardOpen requests for malformed or truncated data.
• Example tcpdump command to capture ENIP traffic: tcpdump -i <interface> port 44818 -w enip_traffic.pcap
• In Wireshark, apply a display filter for CIP ForwardOpen requests: cip.CIPService == 0x54 or cip.CIPService == 0x5B. Look for packets with incomplete or unusually short request data.
• Deploy an intrusion detection system (IDS) like Snort or Suricata with rules to detect malformed CIP ForwardOpen requests. Example Snort rule: alert tcp any any -> any 44818 (msg:"Possible CVE-2026-51537 exploit - malformed CIP ForwardOpen"; content:"|54|"; depth:1; byte_jump:4,0,relative; content:!"|00 00|"; within:2; sid:1000001;)

Since the vulnerability is remotely triggerable without authentication, focus on monitoring external and internal network traffic for suspicious ENIP activity.

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Impact Analysis

This vulnerability can have several impacts if exploited:

• Confidentiality Impact: The out-of-bounds read may allow an attacker to access sensitive memory contents, potentially exposing confidential data.
• Availability Impact: The vulnerability can cause the affected system to crash or behave unpredictably, leading to denial-of-service (DoS) conditions.
• No Integrity Impact: The vulnerability does not allow modification of data or system behavior beyond reading memory and causing crashes.

Since the vulnerability is remotely exploitable without authentication, systems running the affected version of OpENer are at high risk if exposed to untrusted networks.

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Compliance Impact

The impact of this vulnerability on compliance depends on the context in which the affected software is used:

• GDPR: If the affected system processes personal data of EU citizens, a successful exploit could lead to unauthorized access to sensitive information, violating GDPR's confidentiality and data protection requirements. Organizations may face fines or legal consequences if they fail to mitigate the risk.
• HIPAA: If the system is used in a healthcare environment and handles protected health information (PHI), exploitation of this vulnerability could result in unauthorized disclosure of PHI, violating HIPAA's Privacy and Security Rules. This may lead to penalties and mandatory corrective actions.
• Industrial Standards (e.g., IEC 62443): The vulnerability may violate requirements for secure industrial control systems (ICS), particularly those related to network security and access control. Non-compliance could result in operational disruptions or regulatory scrutiny.

Organizations using the affected software should assess their compliance obligations and take steps to mitigate the vulnerability to avoid potential violations.

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Mitigation Strategies

To mitigate this vulnerability, follow these immediate steps:

• Apply the latest patch or update from EIPStackGroup OpENer if available. Check the official repository or vendor advisories for fixes.
• If no patch is available, restrict network access to devices running the vulnerable version of OpENer. Use firewalls or network segmentation to limit exposure to trusted networks only.
• Disable or block unnecessary ENIP/CIP traffic, especially ForwardOpen requests, from untrusted sources. Configure firewalls to drop malformed or suspicious ENIP packets.
• Monitor network traffic for signs of exploitation attempts, such as repeated malformed ForwardOpen requests, and block offending IP addresses.
• Consider deploying an intrusion prevention system (IPS) to automatically block malicious ENIP traffic based on signatures or behavioral analysis.

Since the vulnerability does not require authentication, prioritize network-level protections to prevent unauthorized access to vulnerable devices.

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