Double free in Junos OS - CVE-2026-21918
Published: January 19, 2026
Vulnerability identifier: #VU121664
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-21918
CWE-ID: CWE-415
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote non-authenticated attacker to perform a denial of service (DoS) attack.
The vulnerability exists due to double free error in the flow processing daemon (flowd). A remote non-authenticated attacker can 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.
Affected software
Junos OS
How to mitigate CVE-2026-21918
Install updates from vendor's website.
Junos OS - addressed in versions 22.4R3-S7, 23.2R2-S3, 23.4R2-S4, 24.2R2, 24.4R1