CVE-2021-0239: Juniper Junos OS Evolved

Medium severity, CVSS 6.5. EPSS: 0.4% chance of exploitation in the next 30 days.

In Juniper Networks Junos OS Evolved, receipt of a stream of specific genuine Layer 2 frames may cause the Advanced Forwarding Toolkit (AFT) manager process (Evo-aftmand), responsible for handling Route, Class-of-Service (CoS), Firewall operations within the packet forwarding engine (PFE) to crash and restart, leading to a Denial of Service (DoS) condition. By continuously sending this specific stream of genuine Layer 2 frames, an attacker can repeatedly crash the PFE, causing a sustained Denial of Service (DoS). This issue affects Juniper Networks Junos OS Evolved: All versions prior to 20.4R1-EVO. This issue does not affect Junos OS versions.

Affected products

• Juniper Junos OS Evolved: version 20.4 only

Published 2021-04-22. Last modified 2026-06-17.