Integer Overflow Leading to Stack Buffer Overflow in OpENer

Executive Summary

CVE-2026-51536 is a vulnerability in OpENer version 2.3.0 (commit 76b95cf) related to the parsing of incoming CIP (Common Industrial Protocol) network packets. The issue arises from an inconsistency in how the length parameter is typed across the call stack.

An upstream function calculates the length as an int, but a downstream function expects it to be an EipInt16 (a 16-bit signed integer). When a maliciously crafted packet with specific length fields is processed, this mismatch can cause the length parameter to overflow or be truncated into a negative value.

This negative length bypasses subsequent bounds checking due to signed/unsigned comparison issues. It is then used in memory operations, specifically when reading data in the DecodePaddedEPath function, leading to a Stack Buffer Overflow.

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Detection Guidance

Detecting this vulnerability on your network or system requires monitoring for maliciously crafted CIP (Common Industrial Protocol) packets that exploit the length parameter inconsistency in OpENer 2.3.0.

Since the vulnerability involves a stack buffer overflow during packet parsing, you can use network monitoring tools to inspect CIP traffic for packets with anomalous length fields. Below are some suggested approaches and commands:

• Use Wireshark or tcpdump to capture and analyze CIP traffic. Look for packets with unusually large or negative length values in the CIP header.
• Example tcpdump command to capture CIP traffic on port 44818 (default CIP port): tcpdump -i eth0 -w ciptraffic.pcap port 44818
• Use an intrusion detection system (IDS) like Snort or Suricata with custom rules to detect packets that trigger the signed/unsigned comparison issue. For example, a rule could flag packets where the length field exceeds the expected 16-bit signed integer range.
• If you have access to the OpENer source code or binary, static or dynamic analysis tools (e.g., Valgrind, AddressSanitizer) can help identify memory corruption issues during packet processing.

Note that detecting this vulnerability may require deep packet inspection and familiarity with CIP protocol specifics.

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Impact Analysis

This vulnerability can have severe impacts if exploited.

• Remote attackers can send specially crafted CIP packets to trigger a Stack Buffer Overflow, potentially leading to arbitrary code execution on the affected system.
• The vulnerability does not require authentication (PR:N) and can be exploited over a network (AV:N), making it accessible to attackers without direct access to the system.
• The CVSS v3.1 BaseScore of 9.1 indicates a critical severity, with high impacts on both confidentiality (C:H) and availability (A:H). This means an attacker could gain access to sensitive data or cause the system to crash or become unresponsive.
• Systems running OpENer 2.3.0 in industrial environments, such as those using CIP for communication, are particularly at risk. This could disrupt critical operations or lead to unauthorized control of industrial equipment.

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Compliance Impact

The impact of this vulnerability on compliance with standards and regulations depends on the context in which OpENer is used.

• GDPR: If the affected system processes personal data of EU citizens, a successful exploit could lead to unauthorized access or disclosure of this data. This would violate GDPR requirements for data protection and could result in significant fines or legal consequences.
• HIPAA: In healthcare environments, if the system handles protected health information (PHI), exploitation of this vulnerability could lead to unauthorized access or disruption of PHI. This would violate HIPAA's Security Rule, which mandates the protection of electronic PHI.
• Industrial Standards: For industries governed by standards like IEC 62443 (industrial cybersecurity), this vulnerability represents a failure to implement adequate security measures. Exploitation could lead to non-compliance, especially if the system is part of critical infrastructure.

Organizations using OpENer 2.3.0 should assess whether their systems are exposed to this vulnerability and take corrective actions to maintain compliance with relevant regulations.

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Mitigation Strategies

To mitigate this vulnerability in OpENer 2.3.0, follow these immediate steps:

• Apply the latest patch or update for OpENer if available. Since no resources are provided, check the official OpENer repository or vendor advisories for fixes.
• If no patch is available, restrict network access to the affected OpENer instance. Use firewalls or network segmentation to limit exposure to trusted sources only.
• Disable or block CIP traffic on untrusted networks until a patch is applied. This can be done using firewall rules to drop packets on port 44818 (default CIP port).
• Monitor network traffic for signs of exploitation, such as malformed CIP packets with anomalous length fields, as described in the detection section.
• Consider deploying an intrusion prevention system (IPS) to block malicious packets that attempt to exploit the vulnerability.
• If possible, replace or upgrade the OpENer software to a version that is not affected by this vulnerability.

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