CVE-2026-21921
📋 TL;DR
A Use After Free vulnerability in Juniper's chassis daemon allows authenticated low-privilege attackers to cause denial-of-service by repeatedly subscribing/unsubscribing telemetry collectors. This affects Junos OS and Junos OS Evolved, potentially causing process crashes and system outages until recovery.
💻 Affected Systems
- Juniper Networks Junos OS
- Juniper Networks Junos OS Evolved
📦 What is this software?
Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →Junos by Juniper
Junos OS is Juniper Networks' flagship network operating system running on enterprise routers, switches, security appliances, and data center infrastructure worldwide. Deployed across telecommunications providers, ISPs, cloud service providers, financial institutions, and large enterprises, Junos po...
Learn more about Junos →⚠️ Risk & Real-World Impact
Worst Case
Complete network outage affecting routing, switching, and management functions until system recovers from process crashes.
Likely Case
Intermittent service disruptions as affected processes (chassisd, rpd, mib2d) crash and restart, degrading network performance.
If Mitigated
Limited impact with proper network segmentation and monitoring, though authenticated attackers could still trigger crashes.
🎯 Exploit Status
Requires authenticated access and ability to repeatedly subscribe/unsubscribe telemetry collectors over extended period.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Junos OS: 22.4R3-S8, 23.2R2-S5, 23.4R2 or later; Junos OS Evolved: 22.4R3-S8-EVO, 23.2R2-S5-EVO, 23.4R2-EVO or later
Vendor Advisory: https://kb.juniper.net/JSA106021
Restart Required: Yes
Instructions:
1. Download appropriate Junos OS/Junos OS Evolved patch version. 2. Backup configuration. 3. Install patch via CLI or J-Web interface. 4. Reboot device to apply changes. 5. Verify patch installation.
🔧 Temporary Workarounds
Restrict Telemetry Access
allLimit telemetry subscription capabilities to trusted users only via access control policies.
configure
set system services telemetry access-control-group trusted-group
set system services telemetry access-control-group trusted-group client-list trusted-ips
commit
Monitor Process Health
allImplement monitoring for chassisd, rpd, and mib2d process restarts to detect exploitation attempts.
show system processes extensive | match chassisd|rpd|mib2d
show system core-dumps
🧯 If You Can't Patch
- Implement strict network segmentation to isolate management interfaces from untrusted networks.
- Enforce least privilege access controls and monitor for unusual telemetry subscription patterns.
🔍 How to Verify
Check if Vulnerable:
Check current Junos version: show version | match Junos. Compare against affected versions listed in advisory.Check Version:
show version | match JunosVerify Fix Applied:
Verify installed version is patched: show version | match Junos. Check for absence of process crashes: show system core-dumps.📡 Detection & Monitoring
Log Indicators:
- chassisd/rpd/mib2d process crashes
- frequent telemetry subscription/unsubscription events
- core dump files generated
Network Indicators:
- unusual telemetry protocol traffic patterns
- repeated connection attempts to telemetry ports
SIEM Query:
source="juniper-firewall" AND (process="chassisd" OR process="rpd" OR process="mib2d") AND event="crash"