CVE-2021-0289 : Exploit Details and Defense Strategies

This article provides insights into CVE-2021-0289, a vulnerability in Juniper Networks Junos OS that allows attackers to bypass user-defined ARP Policers.

Understanding CVE-2021-0289

CVE-2021-0289 involves a Time-of-check Time-of-use (TOCTOU) Race Condition vulnerability in Junos OS, impacting certain versions of the software.

What is CVE-2021-0289?

When user-defined ARP Policers are applied on Aggregated Ethernet (AE) interface units, a race condition vulnerability allows an attacker to replace the user ARP Policers with default ones, potentially compromising security.

For Junos OS, versions 5.6R1 and later up to specific releases are affected, with exceptions for certain versions.

The Impact of CVE-2021-0289

The vulnerability poses a medium severity risk with a CVSS base score of 6.5. The attack complexity is low, but the availability impact is high.

Technical Details of CVE-2021-0289

The vulnerability arises due to a race condition between the Device Control Daemon (DCD) and the firewall process (dfwd) in Junos OS.

Vulnerability Description

Attackers can exploit a race condition to bypass user-defined ARP Policers, leading to potential security breaches.

Affected Systems and Versions

Junos OS versions 5.6R1 up to certain releases are impacted, with exceptions listed for specific versions.

Exploitation Mechanism

There is no known malicious exploitation of this vulnerability, as confirmed by Juniper SIRT.

Mitigation and Prevention

To address CVE-2021-0289, Juniper Networks recommends specific software releases for different platforms.

Immediate Steps to Take

For recovery, restart the firewall process to update the ARP Policers on AE interface units.

Long-Term Security Practices

Ensure timely software updates and follow Juniper Networks' recommended versions to prevent potential security risks.

Patching and Updates

Refer to the Juniper Networks advisory JSA11191 for detailed information on software releases addressing CVE-2021-0289.