Out-of-Bounds Read in OpENer CIP Message Parsing

Executive Summary

CVE-2026-51541 is an out-of-bounds read vulnerability in OpENer version 2.3.0 (commit 76b95cf). The issue occurs during CIP (Common Industrial Protocol) message parsing when handling malformed explicit requests.

An attacker can exploit this by sending a valid ENIP (EtherNet/IP) SendRRData frame containing a very short CIP payload. The payload includes a forged EPath size field that falsely claims more path words are present than actually exist in the payload.

The parser trusts the attacker-controlled path_size value and continues decoding path segments without verifying the remaining length of the buffer. This causes the parser to read beyond the end of the stack receive buffer, leading to an out-of-bounds read.

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Detection Guidance

Detecting this vulnerability on your network or system involves monitoring for malformed CIP messages that exploit the out-of-bounds read issue in OpENer 2.3.0. Since the vulnerability is triggered by a forged EPath size in explicit requests, you can look for anomalous ENIP SendRRData frames with unusually short CIP payloads but inflated path_size fields.

• Use network monitoring tools like Wireshark to capture and analyze ENIP/CIP traffic. Filter for SendRRData frames and inspect the CIP payload for discrepancies between the path_size field and the actual length of the path segments.
• Check for unexpected crashes or memory corruption in OpENer instances, which may indicate exploitation attempts. Logs from the application or system may reveal segmentation faults or buffer overflow errors.
• If you have access to the OpENer source code or binary, you can instrument it to log or alert when the path_size field exceeds the remaining buffer length during CIP message parsing.

Example Wireshark filter to identify suspicious SendRRData frames:

• enip.command == 0x006F (SendRRData command code) and cip.path_size > (cip.payload_length / 2)

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Impact Analysis

This vulnerability can have several impacts if exploited:

• Information disclosure: The out-of-bounds read may expose sensitive data from memory, such as credentials, configuration details, or other process information.
• Denial of service: The vulnerability could crash the affected device or service, disrupting industrial operations that rely on OpENer for communication.
• Potential for further exploitation: While this vulnerability does not directly allow code execution, the memory corruption could be leveraged in combination with other vulnerabilities to achieve more severe impacts.

The CVSS v3.1 score of 9.1 (Critical) indicates a high severity, with network-based exploitation possible without authentication or user interaction.

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Compliance Impact

This vulnerability may impact compliance with several standards and regulations, depending on the context in which OpENer is used:

• GDPR (General Data Protection Regulation): If the out-of-bounds read exposes personal data of EU citizens, it could violate GDPR requirements for data protection and breach notification. Organizations may face fines or legal consequences if they fail to mitigate the risk or report incidents.
• HIPAA (Health Insurance Portability and Accountability Act): If OpENer is used in healthcare systems and the vulnerability leads to unauthorized access to protected health information (PHI), it could result in HIPAA violations. Covered entities must ensure the confidentiality, integrity, and availability of PHI.
• Industrial standards (e.g., IEC 62443, NIST SP 800-82): This vulnerability may violate requirements for secure industrial control systems (ICS). Standards like IEC 62443 mandate protections against unauthorized access and memory corruption issues. Failure to address the vulnerability could lead to non-compliance.

Organizations should assess whether this vulnerability affects their systems and take corrective actions to maintain compliance with applicable regulations.

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Mitigation Strategies

To mitigate this vulnerability, follow these immediate steps:

• Upgrade OpENer to a patched version if available. Since the vulnerability is present in OpENer 2.3.0 (commit 76b95cf), check the project's repository or official channels for updates that address this issue.
• If upgrading is not immediately possible, apply network-level protections to filter or block malformed ENIP/CIP traffic. Use firewalls or intrusion prevention systems (IPS) to drop SendRRData frames with suspicious path_size values.
• Isolate systems running OpENer from untrusted networks to reduce exposure to potential attackers. Restrict access to only trusted IP addresses or subnets.
• Monitor network traffic for signs of exploitation attempts, such as repeated SendRRData frames with forged EPath sizes. Set up alerts for unusual activity.
• If you are developing or maintaining OpENer, implement boundary checks during CIP message parsing to ensure the path_size field does not exceed the remaining buffer length. Validate all attacker-controlled inputs before processing.

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