CVE-2026-21920

An Unchecked Return Value vulnerability in the DNS module of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).

If an SRX Series device configured for DNS processing, receives a specifically formatted DNS request flowd will crash and restart, which causes a service interruption until the process has recovered.

This issue affects Junos OS on SRX Series:

• 23.4 versions before 23.4R2-S5,
• 24.2 versions before 24.2R2-S1,
• 24.4 versions before 24.4R2.

This issue does not affect Junos OS versions before 23.4R1.