An Improper Check for Unusual or Exceptional Conditions vulnerability in the Juniper DHCP service (jdhcpd) of Juniper Networks Junos OS and Junos OS Evolved on ACX Series allows a DHCP client in one subnet to exhaust the address pools of other subnets, leading to a Denial of Service (DoS) on the downstream DHCP server.

By default, the DHCP relay agent inserts its own Option 82 information when forwarding client requests, optionally replacing any Option 82 information provided by the client. When a specific DHCP DISCOVER is received in 'forward-only' mode with Option 82, the device should drop the message unless 'trust-option82' is configured. Instead, the DHCP relay forwards these packets to the DHCP server unmodified, which uses up addresses in the DHCP server's address pool, ultimately leading to address pool exhaustion.

This issue affects Junos OS: 

• all versions before 21.2R3-S10,
• from 21.4 before 21.4R3-S12,
• all versions of 22.2,
• from 22.4 before 22.4R3-S8, 
• from 23.2 before 23.2R2-S5, 
• from 23.4 before 23.4R2-S6, 
• from 24.2 before 24.2R2-S2, 
• from 24.4 before 24.4R2, 
• from 25.2 before 25.2R1-S1, 25.2R2.

Junos OS Evolved on ACX Series:

• all versions before 21.4R3-S12-EVO, 
• all versions of 22.2-EVO,
• from 22.4 before 22.4R3-S8-EVO, 
• from 23.2 before 23.2R2-S5-EVO, 
• from 23.4 before 23.4R2-S6-EVO, 
• from 24.2 before 24.2R2-S2-EVO, 
• from 24.4 before 24.4R2-EVO, 
• from 25.2 before 25.2R1-S1-EVO, 25.2R2-EVO.

DHCP Relay must be configured for forward-only to be vulnerable to this issue:
[ forwarding-options dhcp-relay forward-only ] 

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

This issue was seen during production usage.

The following software releases have been updated to resolve this specific issue:
Junos OS 21.2R3-S10, 21.4R3-S12, 22.4R3-S8, 23.2R2-S5, 23.4R2-S6, 24.2R2-S2, 24.4R2, 25.2R1-S1, 25.2R2, 25.4R1, and all subsequent releases.
Junos OS Evolved 21.4R3-S12-EVO, 22.4R3-S8-EVO, 23.2R2-S5-EVO, 23.4R2-S6-EVO, 24.2R2-S2-EVO, 24.4R2-EVO, 25.2R1-S1-EVO, 25.2R2-EVO, 25.4R1-EVO, and all subsequent releases.

This issue is being tracked as 1876407 which is visible on the Customer Support website.

Note: Juniper SIRT's policy is not to evaluate releases which are beyond End of Engineering (EOE) or End of Life (EOL).

There are no known workarounds for this issue.

2026-01-14: Initial Publication
2026-02-05: Clarified that only EVO on ACX Series is affected

• KB16613: Overview of the Juniper Networks SIRT Quarterly Security Bulletin Publication Process [juniper.net]
• KB16765: In which releases are vulnerabilities fixed? [juniper.net]
• KB16446: Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories [juniper.net]
• Report a Security Vulnerability - How to Contact the Juniper Networks Security Incident Response Team