CVE-2026-57027: EX4100 Series, EX4400: With sFlow configured in a VC scenario multicast traffic leads to an FPC crash

A Missing Release of Memory after Effective Lifetime vulnerability in the packet forwarding engine (pfe) of Juniper Networks Junos OS on specific EX Series devices allows an unauthenticated adjacent attacker to cause a Denial-of-Service (DoS).When sFlow is configured in a Virtual Chassis (VC) scenario with EX4100 Series or EX4400 Series devices, multicast traffic which is received on one VC member and sent out on another member leads to a memory leak and ultimately an FPC crash and restart.

Published 8 Jul 2026

Automatic summary from the vendor's CVE record. We haven't written a full analysis of this vulnerability yet.

Affected and fixed versions

Product / branch	Fixed in
Junos OS (EX4100 Series, EX4400 Series) 0	23.2R2-S7 or later
Junos OS (EX4100 Series, EX4400 Series) 23.4	23.4R2-S7 or later
Junos OS (EX4100 Series, EX4400 Series) 24.2	24.2R2-S4 or later
Junos OS (EX4100 Series, EX4400 Series) 24.4	24.4R2 or later

Always confirm against the vendor advisory, which lists every fixed hotfix.

What it is

The leak can be monitored by watching the continuous increase of the buffer values in the output of:

user@host> show chassis fpc This issue affects Junos OS on EX4100 Series and EX4400:

all versions before 23.2R2-S7,
23.4 versions before 23.4R2-S7,
24.2 versions before 24.2R2-S4,
24.4 versions before 24.4R2.

Am I affected?

A system is only affected if sFlow for multicast is explicitly enabled with:

[ forwarding-options sflow egress-multicast enable ]

Workarounds

There are no known workarounds for this issue.

Exploitation

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

KEV status, EPSS score and vendor data refreshed automatically, last on 13 Oct 2026.