CVE-2025-21601 – Juniper Networks Junos OS SRX Series, EX Series, MX240, MX480, MX960, QFX5120 Series J-Web, Captive Portal, 802.1X, Juniper Secure Connect (JSC) Denial of Service (DoS)

An Improper Following of Specification by Caller vulnerability in web management (J-Web, Captive Portal, 802.1X, Juniper Secure Connect (JSC) of Juniper Networks Junos OS on SRX Series, EX Series, MX240, MX480, MX960, QFX5120 Series, allows an unauthenticated, network-based attacker, sending genuine traffic targeted to the device to cause the CPU to climb until the device becomes unresponsive.

Continuous receipt of these packets will create a sustained Denial of Service (DoS) condition.

This issue affects Junos OS: 

* All versions before 21.4R3-S9,
* from 22.2 before 22.2R3-S5,
* from 22.4 before 22.4R3-S4,
* from 23.2 before 23.2R2-S3,
* from 23.4 before 23.4R2-S3,
* from 24.2 before 24.2R1-S1, 24.2R2.

An indicator of compromise is to review the CPU % of the httpd process in the CLI:
e.g.
  show system processes extensive | match httpd  PID nobody       52   0   20M    191M select   2   0:01   80.00% httpd{httpd} <<<<< the percentage of httpd usage if high may be an indicator