CVE-2021-0267
📋 TL;DR
This vulnerability allows an attacker to cause a denial of service (DoS) by sending a specially crafted DHCP packet to Juniper Junos OS devices running the JDHCPD DHCP Relay Agent with active-lease query enabled. The crafted packet triggers improper input validation, crashing the jdhcpd service and potentially creating sustained DoS conditions. This affects Junos OS versions 19.4 through 20.3 (excluding Junos OS Evolved) when configured for broadband subscriber sessions.
💻 Affected Systems
- Juniper Networks Junos OS
📦 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 →⚠️ Risk & Real-World Impact
Worst Case
Sustained denial of service affecting all DHCP services on the device, disrupting broadband subscriber sessions and potentially causing cascading network failures.
Likely Case
Intermittent jdhcpd service crashes requiring manual restarts, causing temporary DHCP service outages for broadband subscribers.
If Mitigated
Limited impact with proper network segmentation and monitoring, allowing quick detection and service restoration.
🎯 Exploit Status
Exploitation requires sending crafted DHCP packets to vulnerable devices, which is relatively straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 19.4R3-S1, 20.1R2-S1, 20.1R3, 20.2R3, 20.3R2 or later
Vendor Advisory: https://kb.juniper.net/JSA11158
Restart Required: Yes
Instructions:
1. Download appropriate Junos OS version from Juniper support portal. 2. Install using 'request system software add' command. 3. Reboot device after installation completes.
🔧 Temporary Workarounds
Disable active-lease query
allDisable the vulnerable active-lease query feature in DHCP Relay Agent configuration
set forwarding-options dhcp-relay active-leasequery disable
Restrict DHCP traffic
allImplement firewall rules to restrict DHCP traffic to trusted sources only
set firewall family inet filter BLOCK-DHCP term TRUSTED from source-address <trusted-networks>
set firewall family inet filter BLOCK-DHCP term BLOCK-ALL then discard
🧯 If You Can't Patch
- Implement strict network segmentation to isolate DHCP traffic
- Deploy intrusion detection/prevention systems to monitor for DHCP anomalies
🔍 How to Verify
Check if Vulnerable:
Check Junos OS version with 'show version' and verify if active-leasequery is enabled with 'show configuration forwarding-options dhcp-relay'Check Version:
show versionVerify Fix Applied:
Verify upgraded version with 'show version' and confirm active-leasequery configuration remains disabled if using workaround📡 Detection & Monitoring
Log Indicators:
- JDHCPD process crashes in system logs
- DHCP service restart messages
- Increased DHCP error rates
Network Indicators:
- Unusual DHCP packet patterns
- DHCP traffic from unexpected sources
- DHCP service unresponsiveness
SIEM Query:
source="junos" AND ("jdhcpd" AND (crash OR restart)) OR ("DHCP" AND anomaly)🔗 References
- https://kb.juniper.net/JSA11158
- https://www.juniper.net/documentation/us/en/software/junos/subscriber-mgmt-sessions/topics/ref/statement/active-leasequery-edit-forwarding-options.html
- https://kb.juniper.net/JSA11158
- https://www.juniper.net/documentation/us/en/software/junos/subscriber-mgmt-sessions/topics/ref/statement/active-leasequery-edit-forwarding-options.html
