CVE-2021-0299

7.5 HIGH

Denial of Service

📋 TL;DR

A vulnerability in Juniper Junos OS allows remote attackers to cause a denial of service by sending specially crafted IPv6 packets. When processed, these packets trigger a kernel crash that forces the device to reboot, creating a sustained DoS condition. Only systems with IPv6 configured running affected Junos OS versions are vulnerable.

💻 Affected Systems

Products:

• Juniper Networks Junos OS

Versions: 19.4 versions prior to 19.4R3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R1-S1, 20.2R2

Operating Systems: Junos OS

Default Config Vulnerable: ✅ No

Notes: Only affects systems with IPv6 configured. Devices with only IPv4 are not vulnerable. Does not affect versions prior to 19.4R1.

📦 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 →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Sustained denial of service causing repeated device reboots, network outages, and potential cascading failures in critical infrastructure.

🟠

Likely Case

Intermittent device crashes and reboots leading to network instability and service disruption.

🟢

If Mitigated

Minimal impact with proper network segmentation, IPv6 filtering, and updated systems.

🌐 Internet-Facing: HIGH - Attackers can send malformed IPv6 packets from the internet to vulnerable devices.

🏢 Internal Only: MEDIUM - Internal attackers or compromised systems could exploit this, but requires IPv6 connectivity.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires sending malformed IPv6 packets to vulnerable devices. No authentication needed.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 19.4R3, 20.1R2, 20.2R1-S1, or 20.2R2

Vendor Advisory: https://kb.juniper.net/JSA11213

Restart Required: Yes

Instructions:

1. Check current Junos OS version. 2. Download appropriate fixed version from Juniper support. 3. Install update following Juniper upgrade procedures. 4. Reboot device to apply changes.

🔧 Temporary Workarounds

Disable IPv6

all

Temporarily disable IPv6 functionality to prevent exploitation

Copy

set system no-ipv6-routing
commit

Filter IPv6 Traffic

all

Implement firewall rules to block or limit IPv6 traffic to vulnerable devices

Copy

set firewall family inet6 filter BLOCK-IPV6 term 1 then discard
commit

🧯 If You Can't Patch

• Implement strict IPv6 traffic filtering at network perimeter
• Segment vulnerable devices and limit IPv6 exposure

🔍 How to Verify

Check if Vulnerable:

Copy

Check Junos OS version and IPv6 configuration: show version | match Junos, show configuration system | match ipv6

Check Version:

Copy

show version | match Junos

Verify Fix Applied:

Copy

Verify Junos OS version is patched: show version | match Junos, confirm version is 19.4R3, 20.1R2, 20.2R1-S1, or 20.2R2

📡 Detection & Monitoring

Log Indicators:

• Kernel panic messages
• Unexpected system reboots
• IPv6 packet processing errors

Network Indicators:

• Unusual IPv6 traffic patterns
• Malformed IPv6 packets
• Device unreachability

SIEM Query:

Copy

source="juniper-firewall" AND ("kernel panic" OR "system reboot" OR "IPv6 error")

📊 Metadata

CVE ID: CVE-2021-0299

CVSS v3 Score: 7.5 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE: CWE-755

Published: October 19, 2021

Last Updated: November 21, 2024

🔗 References

• https://kb.juniper.net/JSA11213 Vendor Advisory
• https://kb.juniper.net/JSA11213 Vendor Advisory

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