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.

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

EPSS: 0.004 (35.1th percentile) — read the EPSS interpretation.

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.

Affected products

Juniper Junos — versions 22.4, 23.2, 23.4
Juniper Mx10004
Juniper Mx10008
Juniper Mx2008
Juniper Mx2010
Juniper Mx2020
Juniper Mx204
Juniper Mx240
Juniper Mx304
Juniper Mx480

Weakness classification (CWE)

CWE-415 — Double Free

References

sirt@juniper.net (vendor-advisory, Vendor Advisory)
sirt@juniper.net (vendor-advisory, Vendor Advisory)

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.