An Improper Check for Unusual or Exceptional Conditions vulnerability in the Juniper DHCP service (jdhcpd) of Juniper Networks Junos OS and Junos OS Evolved 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: 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.