An Improper Handling of Exceptional Conditions vulnerability in route processing of Juniper Networks Junos OS on specific end-of-life (EOL) ACX Series platforms allows an attacker to crash the Forwarding Engine Board (FEB) by flapping an interface, leading to a Denial of Service (DoS).

On ACX1000, ACX1100, ACX2000, ACX2100, ACX2200, ACX4000, ACX5048, and ACX5096 devices, FEB0 will crash when the primary path port of the L2 circuit IGP (Interior Gateway Protocol) on the local device goes down. This issue is seen only when 'hot-standby' mode is configured for the L2 circuit.

This issue affects all versions of Junos OS before 21.2R3-S9 on ACX1000, ACX1100, ACX2000, ACX2100, ACX2200, ACX4000, ACX5048, and ACX5096.

This issue only occurs when an L2 circuit is configured for hot-standby.  For example:

[protocols l2circuit neighbor x.x.x.x interface <intf> backup-neighbor x.x.x.x hot-standby]

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

This issue was seen during production usage.

The following software releases have been updated to resolve this specific issue: 21.2R3-S9.

Note: Support for the ACX2k Series ended with Junos OS 21.2.

This issue is being tracked as 1840825 which is visible on the Customer Support website.

Note: Juniper SIRT's policy is not to evaluate releases which are beyond End of Engineering (EOE) or End of Life (EOL).

There are no known workarounds for this issue.

2025-07-09: Initial Publication

• KB16613: Overview of the Juniper Networks SIRT Quarterly Security Bulletin Publication Process [juniper.net]
• KB16765: In which releases are vulnerabilities fixed? [juniper.net]
• KB16446: Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories [juniper.net]
• Report a Security Vulnerability - How to Contact the Juniper Networks Security Incident Response Team
• https://www.cve.org/CVERecord?id=CVE-2025-52947