Double Free in Juniper Junos

CVE-2026-21918

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.

Vulnerability class: Double Free

Published · last modified .

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.004 (35.0th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 35th percentile — 35.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-21918: held from 0.004 to 0.004.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: -0.000

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-21918?
CVE-2026-21918 is a high-severity vulnerability in Juniper Junos, classified under Double Free. CVSS score: 7.5/10. Published 2026-01-15.
How severe is CVE-2026-21918?
High severity. CVSS v3 base score is 7.5 out of 10.