CVE-2026-21918: Juniper Junos

High severity, CVSS 7.5. EPSS: 0.4% chance of exploitation in the next 30 days.

A Double Free vulnerability in the flow processing daemon (flowd) of Juniper Networks Junos OS on SRX and MX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS). On all SRX and MX Series platforms, when during TCP session establishment a specific sequence of packets is encountered a double free happens. This causes flowd to crash and the respective FPC to restart. This issue affects Junos OS on SRX and MX Series: * all versions before 22.4R3-S7, * 23.2 versions before 23.2R2-S3, * 23.4 versions before 23.4R2-S4, * 24.2 versions before 24.2R2.

Affected products

• Juniper Junos: before 22.4 (fixed in 22.4); version 22.4 only; version 23.2 only; version 23.4 only; version 24.2 only

Published 2026-01-15. Last modified 2026-06-17.