CVE-2021-20596 Explained : Impact and Mitigation

This article provides detailed information about CVE-2021-20596, a vulnerability in MELSEC-F Series FX3U-ENET firmware versions 1.14 and prior that could allow a remote attacker to cause a denial of service (DoS) condition.

Understanding CVE-2021-20596

CVE-2021-20596 is a NULL Pointer Dereference vulnerability in MELSEC-F Series FX3U-ENET firmware versions 1.14 and earlier. It could be exploited by sending specially crafted packets, potentially leading to a DoS condition in communication.

What is CVE-2021-20596?

The CVE-2021-20596 vulnerability affects MELSEC-F Series FX3U-ENET, FX3U-ENET-L, and FX3U-ENET-P502 with firmware version 1.14 and prior. It allows an unauthenticated remote attacker to disrupt communication by exploiting a NULL Pointer Dereference issue.

The Impact of CVE-2021-20596

The vulnerability could result in a DoS condition in communication, affecting the availability of affected systems. However, control by MELSEC-F series PLC is not impacted, and a system reset is necessary for recovery.

Technical Details of CVE-2021-20596

CVE-2021-20596 arises from a NULL Pointer Dereference flaw in MELSEC-F Series FX3U-ENET firmware. The affected versions are susceptible to crafted packets that can trigger the vulnerability.

Vulnerability Description

The vulnerability allows a remote unauthenticated attacker to exploit a NULL Pointer Dereference, potentially leading to a DoS state in communication.

Affected Systems and Versions

MELSEC-F Series FX3U-ENET, FX3U-ENET-L, and FX3U-ENET-P502 firmware versions 1.14 and prior are vulnerable to this issue.

Exploitation Mechanism

By sending specially crafted packets, a remote attacker can trigger the NULL Pointer Dereference flaw, causing a DoS condition in communication.

Mitigation and Prevention

To address CVE-2021-20596, immediate steps should be taken to mitigate the risk and prevent potential exploitation.

Immediate Steps to Take

Implement network segmentation, restrict access to vulnerable systems, and monitor for any unusual network activity to detect potential exploitation.

Long-Term Security Practices

Regularly update firmware and security patches, conduct security assessments, and educate users on cybersecurity best practices to enhance overall resilience.

Patching and Updates

Apply patches provided by the vendor to address the vulnerability and ensure that systems are up-to-date with the latest security fixes.