CVE-2026-21918

moderate-risk

Published 2026-01-15

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.

Do I need to act?

0.02% chance of exploitation

EPSS score — low exploit probability

Not on CISA KEV list

No confirmed active exploitation reported to CISA

Patch status unknown

Check vendor advisories for fix availability and mitigation guidance

CVSS 7.5/10 High

NETWORK / LOW complexity

Affected Products (20)

Junos

Affected Vendors

Juniper

References (2)

Vendor Advisory https://kb.juniper.net/JSA106018

Vendor Advisory https://supportportal.juniper.net/JSA106018

/ 100

moderate-risk

Severity 26/34 · High

Exploitability 0/34 · Minimal

Exposure 23/34 · High